It was ALLAH’S promise to Aadam (Alaihis Salaam) (and his progeny after him) to send guidance to them. ALLAH says: “We said: Go down from it (Paradise) all of you, and when guidance comes to you from ME, then whoever shall follow MY guidance, no fear shall come over them, nor shall they grieve.” [Surah 2:38]
ALLAH’S guidance came in the form of the Prophets and Messengers and in the form of books which ALLAH revealed to HIS Messengers. ALLAH’S guidance as taught by the Messengers and contained in HIS books has always been made up of:
All the Messengers called mankind to believe in ALLAH, HIS Angels. HIS Books, HIS Messengers, the Last Day and Destiny. These six beliefs constitute the basis of the beliefs of every Mu’min. The Qur’aan and Hadith Sharief have summarized these six beliefs and made them criterion for correct and accepted Imaan. ALLAH says: “Oh you who believe, believe in ALLAH and HIS Messenger (Sallallaahu Alaihi Wa Sallam) and the book that HE has revealed to HIS Messenger (Sallallaahu Alaihi Wa Sallam) and the book that HE has revealed before. And whoever disbelieve in ALLAH, HIS Angels, HIS Books, and the Last Day has indeed gone astray.” [Surah 4: 136]
Abu Hurairah (RadhiAllahu Anhu) narrates that the Angel Jibreel (Alaihis Salaam) asked the Messenger (Sallallaahu Alaihi Wa Sallam) what is Imaan? He (Sallallaahu Alaihi Wa Sallam) said: “Imaan is to believe in ALLAH and HIS Angels, and HIS Books, and HIS Messengers, and the Last Day, and to believe Destiny the good and bad of it are from ALLAH”. [Muslim Sharief]
The Messengers and books also called believers to submit themselves to ALLAH in all their actions. For this ALLAH has provided Muslims with a code of conduct otherwise known as Shari’ah. The Shari’ah contains the laws of ALLAH and serves as a guidance for the Muslim in the practical aspects of religion such as Ibaadah or Worship which includes Salaah, Zakaah, Fasting etc. And Mu’aamalaat or legal dealings, such as marriage and trade. Through the Shari’ah, a Muslim comes to know the rights of ALLAH upon him as well as the rights of ALLAH’S creation.