What is the difference between "Islam" and "Iman"?

Islam is the final message from God to mankind. It is therefore the final religious tradition revealed to the Messenger of God Prophet Muhammad and directed to all peoples of every race, and every geographic location. Every previous revelation was given to a certain prophet to be transmitted to a certain people. Islam, in contradistinction, was revealed to the Messenger of God for all people. To this effect God says, “And [thus, O Prophet,] We have sent thee as [an evidence of Our] grace towards all the worlds.”, “We have not sent you otherwise than to mankind at large, to be a herald of glad tidings and a warner; but most people do not understand [this],”, and “Say [O Muhammad]: "O mankind! Verily, I am an apostle of God to all of you.” The Messenger of God confirmed this fact by saying, “all previous prophets were sent to their peoples, and I have been sent to all of mankind.”

Islam is a religious tradition of ease; it avoids hardship as God has stated, “and [He] has laid no hardship on you in [anything that pertains to] religion,” and, “God wills that you shall have ease, and does not will you to suffer hardship.” God has established the outer form of religion on five principles: the two testimonies, the five canonical prayer, alms giving, fasting, and pilgrimage to Mecca. In the creedal level, Islam is based on six pillars: belief in God, the angels, the prophets, God’s revealed books, the Final Day, and destiny good and bad. Branching from these six pillars of faith, further developed matters of creed which are extracted from the commands and prohibitions found in the Shari’ah. These branches of faith can reach up to some seventy as has been mentioned by the Messenger of God.

These principles upon which are based both Islam and Iman can be found in the hadith of Gabriel that is narrated by Umar ibn al- Khattab who said:

As we sat one day with the Messenger of God, a man with pure white clothing and jet black hair came to us, without a trace of traveling upon him, though none of us knew him. He sat down before the Prophet bracing his knees against his, and resting his hands on his legs and said: “Muhammad, tell me about Islam.” The Messenger of God said: “Islam is to testify there is no god but God and that Muhammad is the Messenger of God, and to perform the prayers, give alms, fast Ramadan, and perform the pilgrimage to the House if you find a way.” He said: “You have spoken the truth,” and we were surprised that he should ask and then confirm the answer. Then he said: “Tell me about true faith (Iman),” and the Prophet answered: “It is to believe in God, His angels, His inspired Books, His messengers, the Last Day, and in destiny, its good and bad.” “You have spoken the truth.” He said, “Now tell me about the perfection of faith (Ihsan),” and the Prophet answered: “It is to worship God as if you see Him, and if you see Him not, He nevertheless sees you.” “Tell me of the Hour,” said the visitor, and he was told: “The one questioned knows no more about it than the questioner.” “Then tell me of its portents,” he said, and the Prophet replied: “That the slave women shall give birth to her mistress, and you shall see barefoot, naked, penniless shepherds vying in constructing high buildings.” Then the visitor left. I waited a while, and the Prophet said to me, “Do you know, ‘Umar, who was the questioner?” and I replied, “God and His messenger know best.” He said, “It was Gabriel, who came to you to teach you your religion.”

As for the name Islam it originates from the fact that Islam is a way of submission and surrender to God Most High. Islam therefore calls for the total surrender to God and Him alone, and to cast away any false gods between one and his Creator, even one’s caprice as one can assign partners to God even by following their caprice as the Quran says, “Have you ever considered [the kind of man] who makes his own desires his deity? Could you, then, [O Prophet,] be held responsible for him?” Likewise the Muslim calls on himself to surrender and submit, knowing that God is expansive as the Messenger of God said, “the Muslim is the one who protects his brethren from his own tongue and hands.”

As for the one who gave the religion its name it is God as He stated in His book, “Today have I perfected your religious law for you, and have bestowed upon you the full measure of My blessings, and willed that self-surrender unto Me shall be your religion,” and “the creed of your forefather Abraham. It is He who has named you – in bygone times as well as in this [divine writ] – ‘those who have surrendered themselves to God,’ so that the Apostle might bear witness to the truth before you, and that you might bear witness to it before all mankind.” , and this is one of the unique qualities of Islam that its name was given by the Creator of humankind.

This short answer should suffice in understanding the relationship between Islam and other religions, the integrals of Islam and Iman (faith), and the origins of Islam’s name. God is most high and all knowing.