Allahu ta’ala wants people to live in comfort and peace in the world and to attain endless happiness in the Hereafter. It is for this reason that He has commanded useful things that cause happiness and forbidden harmful things which cause calamity. The first commandment of Allahu ta’ala is to have iman (faith). Having iman is a must for all people. It is obligatory for everyone.
Literally iman means to know a person to be perfect and truthful and to have faith in him. In Islam, iman means to believe the fact that Rasulullah (sall-Allahu ta’ala ’alaihi wa sallam) isAllahu ta’ala’s Prophet; that he is (Nabi), the Messenger chosen by Him, and to say this with the heart; and to believe in brief what he transmitted briefly and to believe in detail what he transmitted in detail from Allahu ta’ala; and to say (the Kalimat ash-shahada) whenever possible. Strong iman is such that, as we know for certain that fire burns, serpents kill by poisoning and we avoid them, we should deem Allahu ta’ala and His attributes great, be fully certain of this by heart, strive for his consent (rida’) and run to His beauty (jamal), and beware of His wrath (ghadab) and torture (jalal). We should firmly inscribe this iman on the heart like an inscription on marble.
Iman means to love everything which Muhammad ’alaihissalam said and to approve, that is to believe, them by heart. Those people who believe in this manner are called Mu’min or Muslim. Each and every Muslim must follow Muhammad ’alaihis-salam. They must walk in the path he guided. His path is the path shown by the Qur’an al-karim. This path is called Islam. To follow him, firstly, it is necessary to have iman, then, to learn the rules of Islam, then, to perform the fards (commandments) and to abstain from harams (forbidden things or acts), then to do sunnats and to abstain from makruhs. After all these, we should try to adapt ourselves to him in mubahs also.