What does belief in the Prophets and Messengers mean in Islam?

Belief in the Messengers is the firm attestation that Allah did send a Messenger to every nation, inviting them to worship Him alone. This belief entails denouncing all gods that are worshipped beside or to the exclusion of Allah. This entails believing that all Messengers were truthful and did convey the Message of Allah to their nation.

Allah sent many Messengers, whose number is known to Him alone. The mercy of Allah and His wisdom require sending Messengers to mankind, inviting them to worship Him alone. He did not bring the creation into existence in vain; hence, believing in Allah entails believing in His Messengers, as mentioned in the Qur'an:

"Those who disbelieve in Allah and His Messengers and want to make distinction between Allah and His Messengers, saying, 'We believe in some and disbelieve in some,' and want to pursue a course in between. It is they who are the real infidels." [Qur'an, an-Nisa 4:150-152]

It is obligatory for all Muslims to believe in all Prophets and Messengers; he who denies one of them, denies all. The first Prophet was Adam peace be upon him and the first Messenger was Nuh peace be upon him, Noah, and the last Prophet and Messenger is Muhammad ﷺ.

Believing in the Messengers of Allah means believing that they were trustworthy in what they conveyed to their people, and that Allah protected them from what would hamper their mission. Amongst the Prophets, the most prominent and steadfast are Nuh peace be upon him, Ibraheem peace be upon him, Abraham, Musa peace be upon him, Moses, Eesa peace be upon him, Jesus, and the Last Prophet Muhammad ﷺ.