In Amos 3:7 It says that "Surely the Lord God will do nothing, but he revealeth his secret unto his servants the prophets" His secrets are things that pertain to our salvation and our spiritual and often times even temperal salvation. God as told prophets that we will not work without one of them on the earth.
Example, he sent Noah to warn of the flood. He sent Moses to give the Ten Commandments. He sent Christ who is the very Son of God, but also still a prophet to teach his people.
In Matthew 16:17-18 it says"...flesh and blood hath not revealed it unto thee, but my Father which is in heaven.... and upon this rock I will build my church;"
The rock of which Christ speaks is the Rock of Revelation. God build his church upon constent comunication to his servents and his people.
April 2nd and 3rd, come listens to a prophets voice. President Thomas S. Monson