This is one of the Shia Usūl al-Dīn (Roots of the Religion).
"Nubuwwah" means "Prophethood" and denotes that God has appointed perfect Prophets and Messengers to teach mankind Gods religion.
Shi'a believe that the prophets and messengers (Adam being the first prophet and Muhammad the last) appointed by God are impeccable and infallible in every aspect (i.e., in their beliefs, thoughts, actions, speech, etc). The Shi'a also believe that their Imams are incarnations of God and therefore divine beings. Current Muslim belief (Ash'ari) is that prophets are only infallible in regards to revelation but can still make mistakes with regards to issues not connected to revelation e.g. the Prophet (saw) once made a mistake regarding how best to sow the seeds for the best harvest.
Shia Islam ( Arabic شيعى follower; English has traditionally used Shiite or Shiite) is the second largest Islamic denomination; some 20-25% of all Muslims are said to follow a Shia tradition. ... The Quran identifies a number of men as prophets of Islam. ...
They believe that God acts according to a purpose or design, and human reason cannot comprehend this design or purpose in its entirety (though man must always strive to understand as much as he can).
"Nubuwwah" means "Prophethood" and denotes that God has appointed perfect Prophets and Messengers to teach mankind Gods religion.
Imamah (Leadership): God has appointed specific leaders to lead and guide mankind — a prophet appoints a custodian of the religion before his demise.
Nubuwwah aimed at this result and when it was accomplished there was no reason for the continuance of this institution.
The purpose of nubuwwah was to serve and safe-guard man's freedom when it was threatened both from within by his unruly selfish passions and from without by the arbitrary power of rulers and priests.
The purpose of the abolition of nubuwwah is to widen the scope of human freedom and to allow man to judge and decide on all questions affecting his life.