The Only Religion in the Sight of Allah
Question

What is the meaning of the verse in which Allah, may He be Exalted, says (interpretation of the meaning): {Indeed, the religion in the sight of Allah is Islam..} [Al `Imran 3:19]?
Praise be to Allah.Islam is the only acceptable religion
Allah, may He be Exalted, says (interpretation of the meaning):
{Indeed, the religion in the sight of Allah is Islam.} [Al `Imran 3:19]
Here He, may He be Glorified and Exalted, tells us that there is no religion that is acceptable to Him except Islam, which means submitting, surrendering and humbling oneself before Allah, may He be Exalted, worshipping Him alone, and believing in Him and in His Messengers, and what they brought from Allah. For each Messenger Allah prescribed a system of law and a method, until He sent the last of them, Muhammad (blessings and peace of Allah be upon him) He sent him to all people, so after him, Allah will not accept any religion from anyone except Islam, which is the religion that he (blessings and peace of Allah be upon him) brought.
Were the previous Prophets Muslims?
The believers who followed the previous prophets were all Muslims in the general sense of the word, and they will enter Paradise by virtue of their Islam. If any of them lived until the coming of our Prophet (blessings and peace of Allah be upon him), nothing will be accepted from him except following our Prophet (blessings and peace of Allah be upon him).
Qatadah (may Allah have mercy on him) said in his commentary on the verse: “Islam means testifying that there is none worthy of worship except Allah, and affirming what [the Prophet (blessings and peace of Allah be upon him)] brought from Allah, which is the religion of Allah that He prescribed and with which He sent His messengers, and to which He guided His allies. He will not accept any other religion and will not grant reward except for it.
Abu Al-`Aliyah (may Allah have mercy on him) said: Islam means sincere devotion to Allah alone , and worshipping Him without associating anything else with Him." (Tafir At-Tabari  6/275)
Commentaries on: {Indeed, the religion in the sight of Allah is Islam}
Ibn Katheer (may Allah have mercy on him) said:
“In the verse (interpretation of the meaning): {Indeed, the religion in the sight of Allah is Islam}, Allah, may He be Exalted, tells us that there is no religion that He will accept from anyone except Islam, which means following the Messengers and that with which Allah sent them at various times, until they ended with Muhammad (blessings and peace of Allah be upon him), at which point all paths to Him were barred except that of Muhammad (blessings and peace of Allah be upon him). So whoever meets Allah after He sent Muhammad (blessings and peace of Allah be upon him) with any religion other than his, it will not be accepted, as Allah, may He be Exalted, says (interpretation of the meaning):
{And whoever desires other than Islam as religion - never will it be accepted from him, and he, in the Hereafter, will be among the losers..} [Al `Imran 3:85]
and He says in this verse, telling us that the only religion that is acceptable to Him is Islam :
{Indeed, the religion in the sight of Allah is Islam.} [Al `Imran 3:19]" (Tafsir Ibn Kathir 2/25)
Ibn Al-Jawzi (may Allah have mercy on him) said:
“Az-Zajjaj (may Allah have mercy on him) said: Din (religion) is a word which refers to everything that Allah has prescribed for people to worship Him thereby and has commanded them to adhere to it, and He will reward them for it.
Our shaykh, ‘Ali ibn ‘Ubaydillah (may Allah have mercy on him) said: Din refers to what a person adheres to and commits himself to for the sake of Allah, may He be Glorified and Exalted.
Ibn Qutaybah (may Allah have mercy on him) said: Islam means entering into submission , by submitting to Allah and following His commands, and it also means surrendering." (Zad Al-Masir  1/267)
As-Sa‘di (may Allah have mercy on him) said:
“The words {the religion in the sight of Allah}, mean: the religion besides which  there is no other religion that Allah approves of and will accept is Islam, which means submitting to Allah alone, outwardly and inwardly, by adhering to what He prescribed on the lips of His Messengers. Allah, may He be Exalted, says (interpretation of the meaning): {And whoever desires other than Islam as religion - never will it be accepted from him, and he, in the Hereafter, will be among the losers.} [Al `Imran 3:85] So whoever follows a religion other than Islam has not truly submitted to Allah, because he has not followed the path that He prescribed on the lips of His Messengers." (Tafsir As-Sa`di  p. 964)
Ibn ‘Uthaymin (may Allah have mercy on him) said:
“Islam, in the general sense of the word, means worshipping Allah by doing what He prescribed from the time when Allah sent the Messengers until the onset of the Hour, as He, may He be Glorified and Exalted, has stated in many verses, which indicates that the teachings of all earlier Prophets were Islam or submission to Allah, may He be Glorified and Exalted.
Allah, may He be Glorified and Exalted, says tells us that Ibrahim said (interpretation of the meaning):
{Our Lord, and make us Muslims [in submission] to You and from our descendants a Muslim nation [in submission] to You.} [Al-Baqarah 2:128]
Islam in the specific sense of the word, after the sending of the Prophet (blessings and peace of Allah be upon him), is limited to that with which Muhammad (blessings and peace of Allah be upon him) was sent, because that with which the Prophet (blessings and peace of Allah be upon him) was sent abrogated all previous religions. Thus the one who follows him is a Muslim and the one who goes against him is not a Muslim. The followers of the Messengers were Muslim at the time of their Messengers, so the Jews were Muslims at the time of Musa (blessings and peace of Allah be upon him), and the Christians were Muslims at the time of ‘Isa (blessings and peace of Allah be upon him) But when the Prophet Muhammad (blessings and peace of Allah be upon him) was sent and they disbelieved in him, then they were not Muslims.
This Islamic religion is the religion that is acceptable to Allah and will benefit the one who follows it. Allah, may He be Glorified and Exalted, says (interpretation of the meaning):
{Indeed, the religion in the sight of Allah is Islam.} [Al `Imran 3:19]
{And whoever desires other than Islam as religion - never will it be accepted from him, and he, in the Hereafter, will be among the losers.} [Al `Imran 3:85]
This Islam is the Islam of which Allah reminded Muhammad (blessings and peace of Allah be upon him) and his ummah that He had blessed them with it, when He, may He be Exalted, said (interpretation of the meaning):
{This day I have perfected for you your religion and completed My favour upon you and have approved for you Islam as religion.} [Al-Ma’idah 5:3]” (Sharh Thalathat Al-Usul, p. 20)
Shaykh Salih Al-Fawzan (may Allah preserve him) said:
“The religion of the Prophets (blessings and peace of Allah be upon them) is one religion, even though the systems of law vary. Allah, may He be Exalted, says (interpretation of the meaning):
{He has ordained for you of religion what He enjoined upon Noah and that which We have revealed to you, [O Muhammad], and what We enjoined upon Abraham and Moses and Jesus - to establish the religion and not be divided therein.} [Ash-Shura 42:13]
{O messengers, eat from the good foods and work righteousness. Indeed, I, of what you do, am Knowing.
And indeed this, your religion, is one religion, and I am your Lord, so fear Me.} [Al-Mu’minun 23:51-52]
The Prophet (blessings and peace of Allah be upon him) said: “We Prophets, our religion is one and the Prophets are like brothers from different mothers.”
The religion of the Prophets is the religion of Islam, and Allah will not accept any other. It is submission to Allah by affirming His oneness, submitting to Him in obedience, and shunning shirk (association of others with Allah) and its people.
Allah tells us that Nuh said (interpretation of the meaning):
{and I have been commanded to be of the Muslims.} [Yunus 10:72]
And He tells us that Ibrahim said (interpretation of the meaning):
{I have submitted [in Islam] to the Lord of the worlds.} [Al-Baqarah 2:131]
And He says regarding Musa (interpretation of the meaning):
{And Moses said, “O my people, if you have believed in Allah, then rely upon Him, if you should be Muslims”} [Yunus 10:84]
And He says the Messiah (interpretation of the meaning):
{And [remember] when I inspired the disciples, "Believe in Me and in My messenger Jesus." They said, "We have believed, so bear witness that indeed we are Muslims [in submission to Allah].} [Al-Ma’idah 5:111]
Allah, may He be Exalted, says regarding the previous Prophets and the Torah (interpretation of the meaning):
{The prophets who submitted [to Allah] judged by it for the Jews.} [al-Ma’idah 5:44]
And Allah tells us that the Queen of Saba’ (Sheba) said (interpretation of the meaning):
{My Lord, indeed I have wronged myself, and I submit with Solomon to Allah, Lord of the worlds.} [An-Naml 27:44]
Thus Islam is the religion of all the Prophets; it is submission to Allah alone, and the one who submits to Him and to anyone else is a polytheist (one who associates others with Allah), whilst the one who does not submit to Him is arrogant. Both those who associate others with Allah and those who are too arrogant to worship Him are disbelievers.
Submission to Allah includes worshipping Him alone, and obeying Him alone. That means obeying Him at all times, by doing what He has enjoined at that time. When Islam first began, Allah commanded the Muslims to face towards Bayt Al-Maqdis (Jerusalem, when praying), then after that, He enjoined them to face towards the Ka`bah. The one who did either action, at the time when it was enjoined, is a Muslim, for religion is obedience, and both actions were acts of worship for Allah, which may take various forms, which in this case had to do with the direction in which the worshipper faced.
Likewise, the religion of the messengers is one, and even though the systems of law and ways, and rituals, may have differed, that does not mean that the religion was not one. This is even applicable in the system of law brought by one Messenger – as we have seen in the change of the Qiblah from Bayt Al-Maqdis to the Ka`bah in the system of law brought by Prophet Muhammad (blessings and peace of Allah be upon him).
So the religion of the prophets is one , even though their systems of law varied. Allah may have prescribed something at one time, for a reason, then prescribed something else at another time, for a reason. So doing what was abrogated, before it was abrogated, was an act of obedience to Allah, but after it was abrogated, it became obligatory to do that which superseded it. So the one who adheres to that which has been abrogated and does not do that which superseded it is not following the religion of Islam, and he is not following any of the Prophets. Hence the Jews and Christians disbelieved, because they adhered to a system of law that had been changed and abrogated.
Allah, may He be Glorified and Exalted, prescribed for each nation that which was appropriate to its situation and its time, which would rectify its condition and serve its best interests. Then Allah abrogated whatever He willed of those systems of law because their time had come to an end, until He sent His Prophet Muhammad, the last of the Prophets, to all the people on earth, for the rest of time until the Day of Resurrection, and He ordained for him a system of law that is comprehensive and is suited to every time and place, which cannot be altered or abrogated. So all the people of Earth have no option but to follow him and believe in him (blessings and peace of Allah be upon him) Allah, may He be Exalted, says (interpretation of the meaning):
{Say, [O Muhammad], “O mankind, indeed I am the Messenger of Allah to you all”.} [Al-A`raf 7:159]” (Al-Irshad ila Sahih Al-I`tiqad, p. 194)
And Allah knows best.