Allah has said “Muhammad is not the father of any man among you but he is the Messenger of Allah and the last of the Prophets. And Allah is Ever All-Aware of everything” (al-Ahzaab 33:40).
Allah has also said
“This day I have perfected your religion for you completed My Favor upon you and have chosen for you Islam as your religion.” (Surah al-Maaidah (5):3)
The Exalted has also said “Truly the religion with Allah is Islam.” (Surah Aali-Imraan (3):19).
Again Allah says “And whoever seeks a religion other than Islam it will never be accepted of him and in the Hereafter he will be one of the losers.” (Surah Aali-Imraan (3):85)
Allah has made it incumbent upon all of humankind that they that this as a religion and means of submission to Allah. In speaking to the Messenger of Allah Allah has said “Say [O Muhammad to the people:] O humankind! Verily I am sent to you all as the Messenger of Allah - to Whom belongs the dominion of the heavens and the earth. None has the right to be worshipped but He. It is He Who gives life and causes death. So believe in Allah and His Messenger the Prophet who can neither read nor write who believes in Allah and His Words and follow him so that you may be guided.” (Surah al-Araaf (7):158)
In Sahih Muslim it is recorded on the authority of Abu Hurairah that the Messenger of Allah said “By the one in whose hand is the soul of Muhammad no one be he Jew or Christian of the people of this nation hears of me and yet dies without believing in what I have been sent with except that he will be from the companions of the Hell-fire.”
Belief in him means to affirm with proper acceptance and compliance and not merely an affirmation [in the mind] everything that he has come with. For this reason Abu Taalib was not a believer in the Messenger although he affirmed everything he brought and even testified that the Prophet’s religion is the best of all religions.
The Islamic religion encompasses all of the goodness that was embodied in previous religions. However it is distinguished by being suitable for all times places and peoples. Allah says while addressing His Messenger “And We have sent down to you (O Muhammad) the Book in truth confirming the Scripture that came before it and as a criterion over it (old Scriptures).” (Surah al-Maaidah (5):48)
The meaning that it is suitable for all times places and peoples is that the one who adheres to it will never go against what is beneficial for the nation in any place or time. In fact it is the thing that makes things right. It does not mean that it is meant to serve any place time or people as some people have tried to twist it to mean.
The Islamic religion is the religion of truth due to which if one abides by it properly Allah will give help and victory over all other religions. Allah has said “He it is Who has sent His Messenger with guidance and the religion of truth to make it victorious over all (other) religions even though the polytheists hate (it).” (Surah as-Saff (61):9)
Allah also says “Allah has promised those among you who believe and do righteous good deeds that He will certainly grant them succession to [the present rulers] in the earth as He granted it to those before them and that He will grant them the authority to practice their religion that which He has chosen for them (i.e. Islam). And He will surely give them in exchange a safe security after their fear [provided] they (believers) worship Me and do not associate anything [in worship] with Me. But whoever disbelieved after this they are the evildoers.” (Surah an-Noor (24):55)
The Islamic religion is both a matter of creed as well as law. It is complete both in its beliefs and its laws.
It enjoins the oneness of Allah and prohibits associating partners with Allah.
It enjoins truthfulness and prohibits lying and falsehood.
It enjoins justice and prohibits injustice.
It enjoins fulfilling trusts and prohibits treachery.
It enjoins fulfilling promises and prohibits deception.
It enjoins being dutiful to one’s parents and forbids being disobedient to them.
It enjoins being good to one’s neighbors and prohibits harming them.
In general one can say that Islam enjoins every noble and virtuous character while prohibiting every evil harmful trait. It enjoins every good pious act and prohibits every evil deed. Indeed Allah has said “Verily Allah enjoins justice and goodness and giving (help) to kith and kin; and forbids all evil deeds bad conduct and wrongdoing. He admonishes you that you may take heed.” (Surah an-Nahl (16):90)