A Christian is asking what is written on the gate of Paradise?
Question

                What is written on the gates of paradise?.
Praise be to Allah.
    Firstly: 

    Paradise does not have only one gate, rather it has many 
    gates. Allaah says (interpretation of the meaning): 

    “And those who kept their duty to their Lord (Al-Muttaqoon 
    – the pious) will be led to Paradise in groups till when they reach it, and 
    its gates will be opened (before their arrival for their reception) and its 
    keepers will say: Salaamun ‘Alaykum (peace be upon you)! You have done well, 
    so enter here to abide therein”

    [al-Zumar 39:73]
There is also evidence 
    narrated in the Sunnah which points to the number of these gates. For 
    example, the Prophet  (peace and blessings of Allaah be upon him) said: 
    “In Paradise there are eight gates, among which is a gate called al-Rayyaan, 
    through which no one will enter except those who fast.” Narrated by 
    al-Bukhaari, 3257; Muslim, 1125. This hadeeth indicates that the number of 
    gates is eight. 

    Secondly: 

    There are some reports which speak of what is written on the 
    gate of Paradise. The strongest report that we have found is that which was 
    narrated by al-Tabaraani and al-Bayhaqi from Abu Umaamah (may Allaah be 
    pleased with him), that the Prophet  (peace and blessings of Allaah be 
    upon him) said: “A man entered Paradise and saw written on its gate ‘Charity 
    receives a tenfold reward and a loan an eighteenfold reward.’” 

    Classed as hasan by al-Albaani. See Saheeh al-Targheeb 
    wa’l-Tarheeb, 1/537. 
Although some scholars 
    were inclined to accept the attribution of this hadeeth to the Prophet  
    (peace and blessings of Allaah be upon him), others – including Ibn 
    al-Jawzi, al-‘Iraaqi, al-Manaawi and others – classed it as da’eef (weak), 
    because the narrators who transmitted it from the Prophet  (peace and 
    blessings of Allaah be upon him) include a narrator who is very weak. 

    There is another report which says: “Written on the gates of 
    Paradise is: ‘Laa ilaaha ill-Allaah Muhammad Rasool-Allaah ‘Ali akhoo 
    rasool-Illaah (There is no god but Allaah, Muhammad is the Messenger of 
    Allaah, ‘Ali is the brother of the Messenger of Allaah).’ This was written 
    two thousand years before the creation of the heavens and the earth.” 

    But this is a false report which cannot be attributed to the 
    Messenger of Allaah  (peace and blessings of Allaah be upon him). See 
    al-Silsilah al-Da’eefah, vol. 10, no. 4901. 
We should also note that 
    speaking about this topic or similar topics that have to do with Paradise, 
    Hell or other matters of the unseen cannot be accepted as correct unless it 
    is based on revelation (wahy) that is proven to be from Allaah, on the lips 
    of His Messenger. 

    And we have to ask ourselves: what is the practical benefit 
    of knowing such things? What good things will we be missing out on if we do 
    not know this? 

    The question which we should really be asking is: How can we 
    get to those gates? How can they be opened for us? How can we enter them? 

    This is the decisive question which people should concern 
    themselves with. 

    In truth there is only one way to reach Paradise: the 
    straight path in which there is no crookedness. Allaah says (interpretation 
    of the meaning): 

    “And verily, this is My straight path, so follow it, and 
    follow not (other) paths, for they will separate you away from His path. 
    This He has ordained for you that you may become Al‑Muttaqoon (the pious)”

    [al-An’aam 6:153]

    The first step on that straight path is believing that there 
    is no god but Allaah and that Muhammad is the Messenger of Allaah, believing 
    that Muhammad  (peace and blessings of Allaah be upon him) is a Prophet 
    and Messenger from Allaah. This is the matter concerning which Allaah took 
    the covenant and pledge from the Prophets before they were sent. Allaah says 
    (interpretation of the meaning):  
“And (remember) when 
    Allaah took the Covenant of the Prophets, saying: ‘Take whatever I gave you 
    from the Book and Hikmah (understanding of the Laws of Allaah), and 
    afterwards there will come to you a Messenger (Muhammad) confirming what is 
    with you; you must, then, believe in him and help him.’ Allaah said: ‘Do you 
    agree (to it) and will you take up My Covenant (which I conclude with you)?’ 
    They said: ‘We agree.’ He said: ‘Then bear witness; and I am with you among 
    the witnesses (for this).’”

    [Aal ‘Imraan 3:81]

    Allaah called all of those who were given a book before him 
    to believe in this final Prophet and His plain Book. Allaah says 
    (interpretation of the meaning): 
“O people of the 
    Scripture (Jews and Christians)! Now has come to you Our Messenger 
    (Muhammad) explaining to you much of that which you used to hide from the 
    Scripture and pass over (i.e. leaving out without explaining) much. Indeed, 
    there has come to you from Allaah a light (Prophet Muhammad) and a plain 
    Book (this Qur’aan). 
16. Wherewith Allaah 
    guides all those who seek His Good Pleasure to ways of peace, and He brings 
    them out of darkness by His Will unto light and guides them to the Straight 
    Way (Islamic Monotheism)”
[al-Maa'idah 5:15-16] 

    Allaah tells us that His proof is established against the 
    People of the Book and others by means of this final Prophet. Allaah says 
    (interpretation of the meaning): 
“O people of the 
    Scripture (Jews and Christians)! Now has come to you Our Messenger 
    (Muhammad) making (things) clear unto you, after a break in (the series of) 
    Messengers, lest you say: ‘There came unto us no bringer of glad tidings and 
    no warner.’ But now has come unto you a bringer of glad tidings and a 
    warner. And Allaah is Able to do all things”
[al-Maa’idah 5:19] 

    After he has come, no one can enter Paradise unless they 
    follow him and obey him. 

    It was narrated that Jaabir ibn ‘Abd-Allaah (may Allaah be 
    pleased with him) said: Some angels came to the Prophet while he wassleeping. Some of them said, “He is sleeping.” Otherssaid, “His eyes are sleeping but his heart is awake.” Then they said, 
    “There is an example for this companionof yours.” 
    One of them said, “Then set forth an examplefor 
    him.” Some of them said, “He is sleeping.” Theothers 
    said, “His eyes are sleeping but his heart is awake.” Then they said, “His 
    example is that of a manwho has built a house and 
    then offered therein abanquet and sent a messenger 
    to invite thepeople. So whoever accepted the 
    invitation of themessenger, entered the house and 
    ate of the banquet, andwhoever did not accept the 
    invitation of the messenger, didnot enter the house, 
    nor did he eat of the banquet.” Then the angels 
    said, “Explain this example to him sothat he may 
    understand it.” Some of them said, “He issleeping.” 
    The others said, “His eyes are sleeping buthis heart 
    is awake.” And then they said, "Thehouse stands for 
    Paradise and the caller isMuhammad; and whoever 
    obeys Muhammad, obeysAllaah; and whoever disobeys 
    Muhammad, disobeysAllaah. Muhammad separated the 
    people (i.e., throughhis message, the good are 
    distinguished from the badand the believers from the 
    disbelievers).”  

    Saheeh al-Bukhaari, 2861. 

    According to a report narrated by al-Daarimi: Rabee’ah 
    al-Jurashi said: Some (angels) came to the Prophet  (peace and blessings 
    of Allaah be upon him) and it was said to him: “Let your eyes sleep and let 
    your ears hear and let your heart understand.” He said: “My eyes slept but 
    my ears heard and my heart understood.” He said: “It was said to me: A 
    master built a house, then he prepared a banquet and sent a caller (to 
    invite people). Whoever responded to the caller entered the house and ate of 
    the banquet and the master was pleased with him, and whoever did not respond 
    to the caller did not enter the house or eat of the banquet, and the master 
    was angry with him.” Allaah is the master, Muhammad is the caller, the house 
    is Islam and the banquet is Paradise.”  

    Sunan al-Daarimi, 11. 

    If you want to study some of the foretelling of the coming of 
    the Prophet Muhammad  (peace and blessings of Allaah be upon him) that 
    is mentioned in the Torah and Gospel (the Bible), you can refer to the book
    Izhar al-Haqq by Shaykh Rahmatullah al-Hindi. 
May Allaah guide us and 
    you to His Straight Path, the path of those on whom Allaah has bestowed His 
    grace, not the path of those who have earned His anger nor of those who went 
    astray.