God Himself and clearly mentioned in the final scripture which He revealed to man. In the final revelation, called the Qur'an in Arabic, Allah states the following:
"This day have I perfected your religion for you, completed My favour upon you, and I have chosen for you Islam as you religion." (Qur'an 5:3)
"If anyone desires a religion other than Islam (submission to God), never will it be accepted of him." (Qur'an 3:85)
If we investigate the legislations and divine books of heavenly religions, we see that Islam is the purest and the most perfect amongst them all in all aspects and fields religions mentioned.
1- It has the purest faith because it assured the pure monotheism and it keeps God away from all human features and from residing in man or immanentism or uniting with any creature or lack of ability to behave and attributes to Him every perfection that is suitable for His divine essence such as glorification, highness, ability, majesty and others.
2- Islam described all prophets that they are chosen and perfect people and they have great amount of intelligence, cleverness, eloquence, fluency, honesty and intuition, despite all of this they are still people, their highest degree is as God says: “Say: I am but a man like yourselves, (but) the inspiration has come to me” Surat Al-Kahf, Verse 110.
3- Islam is the only one amongst heavenly religions that set perfect balanced legislations that organize working in this life and also good deeds that lead to happiness in the hereafter. A Muslim is a moderate man, he works for his life to dwell it as if he is living forever, and he also prepares good deeds for the hereafter as if he is going to die tomorrow.
4- Islam doesn’t order Muslims by monasticism or to abandon working in this life or to become engrossed totally in this life and forget death and the hereafter but it asks them to be moderate in all the works of this life and the hereafter, God says: “Thus, have We made of you an Ummat (nation) justly balanced” Surat All-Bakara, Verse 143.
5- The divine book of Muslims which is the noble Koran is the only book that is protected from any changes or distortions, God says: “We have, without doubt, sent down the Message; and We will assuredly guard it (from corruption)” Surat Al-Hijr, Verse 9. But the other books of other heavenly religions was changed and perverted by their people, so now we see the four bibles authorized by the church were chosen from four hundred different bibles.
6- Islam made a Muslim directly connected to his Lord, he doesn’t need an intercessor like clergymen or monks or bishops. A Muslim can also worship his God at any place and any time, the prophet (Blessings and peace of Allah be upon him) said: “The ground has been made a mosque and pure for me.” Good deeds and acts of worship not only done at hermitages or temples or monasteries or churches as in other religions.
7- If a Muslim did a sin or something wrong and he wants to repent, he goes directly to his Lord and no human can decide to accept his repentance or not.
8- Islam is the only legislation that brings what man needs all over his life in personal status, in inheritance, in dealings, in international politics even the simplest things he needs, everything is mentioned in details.
For all those reasons and others we see that Islam has more general principles, more inclusive legislations and more perfect acts of worship than all other religions so we chose it.