Imamah means "leadership" and is a concept in Twelver theology. The Twelve Imams are the spiritual and political successors to Muhammad, the Prophet of Islam, in the Twelver branch of Shia Islam. According to Twelver theology, the successors to Muhammad are infallible human beings, who not only rule justly over the community, but are also able to maintain and interpret sharia and undertake the esoteric interpretation of the Quran. The words and deeds of Muhammad and the Imams are a guide and model for the community to follow. For this, the Imams must be free from error and sin and chosen by divine decree—nass—through the Prophet.