Which comes first: faith or submission to God, and why?

The Prophet, peace and blessings be upon him, differentiated between Islam and Iman (faith) in the Hadith (definition) of Jibril, making Islam pertain to outward deeds and Iman to inner belief. Some scholars have posited that Islam is the word and Iman is the action, while others have held them to be one and the same. The root of Iman is affirmation, and the root of Islam is submission and obedience. Thus, every believer (mu'min) is a Muslim, but not every Muslim is a believer (mu'min). Islam comes first, and then it must be accompanied by Iman for the religion to be acceptable to Allah.