Prophethood in Islam:
Prophethood is one of the articles of faith in Islam. Hence, if someone does not believe in prophethood, he goes out of the fold of Islam.
Prophethood means that Allah chose pure human beings as guides to call people to the true path of Allah. All people in all areas had their prophets and they were sent with the language of the people they were sent in:
And every nation had a messenger; so when their messenger came, the matter was decided between them with justice and they shall not be dealt with unjustly (Qur'an 10:47)
And We did not send any messenger but with the language of his people, so that he might explain to them clearly; then Allah makes whom He pleases err and He guides whom He pleases and He is the Mighty, the Wise (Qur'an 14:4)
As is seen from the verses above, prophets were sent so that they could clearly explain to their people the message of Allah.
Muslims believe in all the prophets sent by Allah starting with Adam (peace be upon him) and ending with Muhammad (peace be upon him). Final revelation from Allah was given to Prophet Muhammad (peace be upon him), as such, he was the last of messengers:
Muhammad is not the father of any of your men, but he is the Messenger of Allah and the Last of the prophets; and Allah is cognizant of all things (Qur'an 33:40)
Muslims are required to follow whatever Prophet Muhammad (peace be upon him) commanded them to follow and abstain from whatever he has forbidden them from:
Whatever the Messenger gives you, accept it, and from whatever he forbids you, keep back, and be careful of (your duty to) Allah; surely Allah is severe in retributing (evil) (Qur'an 59:7)
So, a Muslim not only follows what is found in the Holy Qur'an but he also faithfully follows the instructions from Prophet Muhammad (peace be upon him). Obedience to Prophet Muhammad (peace be upon him) is as important as obedience to Allah:
And it behoves not a believing man and a believing woman that they should have any choice in their matter when Allah and His Messenger have decided a matter; and whoever disobeys Allah and His Messenger, he surely strays off a manifest straying (Qur'an 33:36)