What Is the Meaning of Belief in Allah?
Question

I have read and heard a great deal about the virtues of attaining true belief in Allah, and I would like you to explain to me in detail the meaning of belief in Allah in a way that will help me to attain true faith and to keep away from everything that goes against the teachings of our Prophet Muhammad (peace and blessings of Allah be upon him) and the way of his companions.
Praise be to Allah.Meaning of belief in Allah
Faith in Allah means believing firmly in His existence, Lordship and Divinity, and in His Names and Attributes. 
Four things necessary for achieving belief in Allah 
Faith in Allah implies four things, whoever believes in them is a true believer. 
1 – Belief in the existence of Allah. 
The existence of Allah is something indicated by reason and by man's innate nature, let alone the large amount of shar’i (revelatory) evidence to that effect. 
(1) The evidence of man’s innate nature that Allah exists: every man has been created with an innate belief in his Creator without having to first think about it or be taught, and no one deviates from this innate nature except the one who has been exposed to misguiding influences. Hence the Prophet (peace and blessings of Allah be upon him) said: “There is no child who is not born in a state of fitrah (the natural inclination of man), but his parents make him a Jew, a Christian or a Magian.” Narrated by al-Bukhaari, 1358; Muslim, 2658.
(2) The evidence of reason that Allah exists: all these created things, past, present and future, must have a Creator Who brought them into existence, because it is not possible for them to have created themselves or to have come into existence by accident.
It is impossible for them to have come into existence by themselves because a thing cannot create itself: before it existed it was non-existent, so how could it be a creator?! And it is impossible for them to have come into existence by accident, because everything that happens must have a cause. Moreover, this creation is done in a wondrous and precise manner, and every created being is in harmony with the rest of creation, and there is a strong connection between cause and effect. All of this makes it impossible that this universe could have come into being accidentally, because what happens accidentally does not happen in a precise and perfect manner, so how could it remain so precisely balanced?  
If it is not possible for these things to have created themselves or to have come into existence by accident, then there must be One Who brought them into existence, namely Allah the Lord of the Worlds. 
Rational evidence and definitive proof of the existence of Allah in the Qur’an
Allah has mentioned this rational evidence and definitive proof in Surat al-Toor, where He says (interpretation of the meaning): 
“Were they created by nothing? Or were they themselves the creators?” [al-Toor 52:35]
They were not created without a Creator, and they did not create themselves, so their Creator must be Allah, may He be blessed and exalted. Hence when Jubayr ibn Mut’im heard the Messenger of Allah (peace and blessings of Allah be upon him) reciting Soorat al-Toor, and he reached these verses (interpretation of the meaning):
“Were they created by nothing? Or were they themselves the creators?
 Or did they create the heavens and the earth? Nay, but they have no firm Belief.
Or are with them the treasures of your Lord? Or are they the tyrants with the authority to do as they like?” [al-Toor 52:35-37]
Jubayir was a mushrik at that time, and said: “My heart almost soared, and that was the first moment that faith entered my heart.” (Narrated by al-Bukhaari in several places. )
We will give you an example that will help to explain that:  
If a person were to tell you of a beautiful palace, surrounded by gardens among which rivers flowed, filled with furniture and couches, decorated with all kinds of luxuries and adornments, and told you that this palace and all that it contains created itself, or came into existence like that by accident without anyone building it, you would hasten to deny that and regard it as a lie, and you would regard this as foolish speech. So after that can it be possible that this wondrous, vast and well balanced universe with its earth, heavens and stars, could have created itself or come into being by accident with no Creator?! 
This rational evidence was understood by a Bedouin who lived in the desert and who expressed it most eloquently, when he was asked, “How do you know your Lord?” He said: “If you see the camel dung you know that a camel has passed this way, and if you see a footstep you know that a person has passed this way, so the heaven with its stars and the earth with its mountain passes and the oceans with their high waves all point to the existence of the All-Hearing, All-Seeing.” 
2 – Belief in the Lordship of Allah 
We mean the belief that He alone is the Lord, with no partner or helper. 
The Lord (Rabb) is the One Who has the power of  creation, dominion and control. There is no Creator except Allah, no Sovereign except Allah, no controller of affairs except Allah. Allah says (interpretation of the meaning): 
“Surely, His is the creation and commandment” [al-A’raaf 7:54] 
“Say (O Muhammad): ‘Who provides for you from the sky and the earth? Or who owns hearing and sight? And who brings out the living from the dead and brings out the dead from the living? And who disposes the affairs?’ They will say: ‘Allah.’ Say: ‘Will you not then be afraid of Allah’s punishment (for setting up rivals in worship with Allah)?’”[Yoonus 10:31] 
“He manages and regulates (every) affair from the heavens to the earth; then it (affair) will go up to Him” [al-Sajdah 32:5] 
“Such is Allah, your Lord; His is the kingdom. And those, whom you invoke or call upon instead of Him, own not even a Qitmeer (the thin membrane over the date stone)” [Faatir 35:13]
Think about what Allah says in Soorat al-Faatihah (interpretation of the meaning): 
“The Only Owner (and the Only Ruling Judge) of the Day of Recompense (i.e. the Day of Resurrection) [Maaliki Yaawm il-deen]” [al-Faatihah 1:4]
And there is an alternative reading, Maliki yawm il-deen. If we  combine the two readings we will see a wondrous meaning, for the Malik (King) has more power and authority than the Maalik (Owner), but a king may sometimes be a king in name only, with no control over affairs, in which case he is a king but not an owner. But as Allah is both Malik and Maalik, then this is confirmation both of His Sovereignty and His control over all affairs. 
3 – Belief in His Divinity 
We mean the belief that He is the One True God, with no partner or associate. 
Allaah (God) means the One Who is loved, i.e., the One Who is worshipped out of love and veneration. This is what is meant by Laa ilaaha ill-Allah (there is no god but Allah), i.e., there is none who is rightfully worshipped except Allah. Allah says (interpretation of the meaning): 
“And your Ilaah (God) is One Ilaah (God — Allah), Laa Ilaaha illa Huwa (there is none who has the right to be worshipped but He), the Most Gracious, the Most Merciful” [al-Baqarah 2:163] 
“Allah bears witness that Laa ilaaha illa Huwa (none has the right to be worshipped but He), and the angels, and those having knowledge (also give this witness); (He always) maintains His creation in justice. Laa ilaaha illa Huwa (none has the right to be worshipped but He), the All-Mighty, the All-Wise” [Aal ‘Imraan 3:18]
Everything that is taken as a god alongside Allah and worshipped instead of Him, its divinity is false. Allah says (interpretation of the meaning): 
“That is because Allah He is the Truth (the only True God of all that exists, Who has no partners or rivals with Him), and what they (the polytheists) invoke besides Him, it is Baatil (falsehood). And verily, Allah He is the Most High, the Most Great” [al-Hajj 22:62]
Calling them gods does not give them the rights of divinity. Allah says (interpretation of the meaning): 
“They are but names which you have named you and your fathers for which Allah has sent down no authority” [al-Najm 53:23]
Allah tells us that Yoosuf (peace be upon him) said to the prison guard (interpretation of the meaning): 
“Are many different lords (gods) better or Allah, the One, the Irresistible?
You do not worship besides Him but only names which you have named (forged) — you and your fathers — for which Allah has sent down no authority” [Yoosuf 12:39-40]
No one deserves to be worshipped or singled out for worship except Allah, and no one has any share in this right with Him, no angel who is close to Him nor any Prophet who was sent. Hence the call of all the Messengers, from the first to the last of them, was the call to say Laa ilaaha ill-Allah. Allah says (interpretation of the meaning): 
“And We did not send any Messenger before you (O Muhammad) but We revealed to him (saying): Laa ilaaha illa Ana [none has the right to be worshipped but I (Allah)], so worship Me (Alone and none else)” [al-Anbiya’ 21:25] 
“And verily, We have sent among every Ummah (community, nation) a Messenger (proclaiming): “Worship Allah (Alone), and avoid (or keep away from) Taaghoot (all false deities, i.e. do not worship Taaghoot besides Allah)” [al-Nahl 16:36]
But the mushrikeen (polytheists) rejected that and took other gods instead of Allah, which they worshipped alongside Allah, seeking their support and help. 
4 – Belief in His Names and Attributes
We mean affirming the names and attributes which Allah has affirmed for Himself in His Book and in the Sunnah of His Messenger (peace and blessings of Allah be upon him) in a manner that befits Him, without distorting or denying the meanings, or asking how, or likening Him to His creation. Allah says (interpretation of the meaning): 
“And (all) the Most Beautiful Names belong to Allah, so call on Him by them, and leave the company of those who belie or deny (or utter impious speech against) His Names. They will be requited for what they used to do” [al-A’raaf 7:180]
This verse indicates that the Most Beautiful names belong to Allah.
And Allah says (interpretation of the meaning): 
“His is the highest description (i.e. none has the right to be worshipped but He, and there is nothing comparable unto Him) in the heavens and in the earth. And He is the All-Mighty, the All-Wise” [al-Room 30:27]
This verse indicates that the attributes of perfection belong to Allah, because “the highest description” is the attribute of perfection. These two verses prove that the most beautiful Names and the most sublime attributes belong to Allah in general terms. With regard to the details of that, there is a great deal of information in the Qur’aan and Sunnah. 
This field of knowledge, i.e., the names and attributes of Allah, is one of the fields in which there has been a great deal of dispute and division among the ummah, and the ummah has split into various factions regarding the names and attributes of Allah.  
Our attitude towards these differences is that enjoined by Allah when He said (interpretation of the meaning): 
“(And) if you differ in anything amongst yourselves, refer it to Allah and His Messenger, if you believe in Allah and in the Last Day” [al-Nisa’ 4:59]
We refer this dispute to the Book of Allah and the Sunnah of His Messenger (peace and blessings of Allah be upon him), seeking guidance therein from the way in which the righteous salaf (predecessors), the Sahaabah (Companions)and Taabi’een (generation after the Companions), understood these verses and ahaadeeth, for they are the most knowledgeable of this ummah as to what Allah and His Messenger meant. ‘Abd-Allah ibn Mas’ood spoke the truth when he described the companions of the Prophet (peace and blessings of Allah be upon him) by saying: “Whoever wants to follow a path, let him follow the path of one who has died, for there is no guarantee that the one who is still alive will not be tempted. Those are the companions of Muhammad (peace and blessings of Allah be upon him), the most pure in heart  of this ummah and the most deep in knowledge, the least sophisticated and complicated, people whom Allah chose to establish His religion and accompany His Prophet. So acknowledge their rights and adhere to their guidance, for they are following true guidance.”
Everyone who deviates from the path of the salaf in this matter is erring and going astray, and is following a path other than that of the believers, so he deserves the warning issued in the verse where Allah says (interpretation of the meaning): 
“And whoever contradicts and opposes the Messenger (Muhammad) after the right path has been shown clearly to him, and follows other than the believers’ way, We shall keep him in the path he has chosen, and burn him in Hell — what an evil destination!” [al-Nisa’ 4:115]
Allah has stipulated that in order to be correctly guided, we must believe what the companions of the Prophet (peace and blessings of Allah be upon him) believed, as He says (interpretation of the meaning): 
“So if they believe in the like of that which you believe then they are rightly guided” [al-Baqarah 2:137] 
Everyone who deviates and wanders far from the path of the salaf is lacking in guidance to the extent that he strays from the path of the salaf. 
Based on this, then what we must do in this case is to affirm what Allah has affirmed for Himself or what His Messenger (peace and blessings of Allah be upon him) has affirmed of the divine names and attributes; we should take the texts of the Qur’aan and Sunnah at face value, and believe in them as the companions of the Prophet (peace and blessings of Allah be upon him) did, as they are the best and most knowledgeable of this ummah (may Allah be pleased with them). 
Four things to be avoided regarding belief in Allah’s Names and Attributes
But it should be noted that there are four things to be avoided, whoever falls into one of them has not attained true belief in the names and attributes of Allah as he is obliged to do. Belief in the names and attributes of Allah is not correct unless one avoids these four things, which are: tahreef (distortion), ta’teel (denial), tamtheel (likening Allah to His creation) and takyeef (asking or discussing how).  
Hence we say that what is meant by belief in the names and attributes of Allah is “affirming the names and attributes which Allah has affirmed for Himself in His Book and in the Sunnah of His Messenger (peace and blessings of Allah be upon him) in a manner that befits Him, without distorting or denying the meanings, or asking how, or likening Him to His creation.” 
There follows a brief explanation of these four things that are to be avoided: 
1.      Tahreef (distorting)
What is meant is changing the meaning of the texts of the Qur’aan and Sunnah from their true meaning, which means affirming that the most beautiful names and sublime attributes belong to Allah, to another meaning which was not intended by Allah or His Messenger (peace and blessings of Allah be upon him). 
For example: 
They distort the meaning of the Hand of Allah which is mentioned in many texts and say that it refers to His blessing or power. 
2.                Ta’teel (denying)
What is meant is denying the beautiful names and sublime attributes and saying that Allah does not possess them or some of them. 
Everyone who denies one of the names or attributes of Allah that are proven in the Qur’aan or Sunnah does not truly believe in the names and attributes of Allah.
3.                Tamtheel (likening Allah to His creation)
This means likening the attribute of Allah to the attribute of a human being, such as saying that Allah’s Hand is like a man’s hand, or that Allah hears as a man hears, or that Allah rose over the Throne like a man sitting on a chair… and so on. Undoubtedly likening the attributes of Allah to the attributes of His creation is wrong and false. Allah says (interpretation of the meaning): 
“There is nothing like Him, and He is the All-Hearer, the All-Seer” [al-Shoora 42:11]
4.                Takyeef (discussing how)
This means discussing how the attributes of Allah are, whereby a person tries to imagine or put into words how the attributes of Allah are. 
This is definitely invalid, and man cannot know this. Allah says (interpretation of the meaning): 
“but they will never encompass anything of His Knowledge” [Ta-Ha 20:110]
Whoever attains these four things believes truly in Allah. 
We ask Allah to make us steadfast in faith and cause us to die therein. 
And Allah knows best. 
Reference:
Risaalat Sharh Usool al-Eemaan by Shaykh Ibn ‘Uthaymeen