A Prophet is someone who represents our Heavenly Father on the Earth and holds all of the Priesthood Keys and the Authority required to govern His church. They are a Mouthpiece for God.
Why does God call Prophets?
God doesn't want anyone to fall short of their potential. God will also not cause us to do something that we shouldn't by not telling us that we shouldn't do it, Therefore God speaks to His chosen Prophet and that individual then tells the world what is supposed to take place.
What does a Prophet do?
A Prophet receives Direct revelation from our Heavenly Father and then tells others the Word of the Lord. The Prophet is also the specific individual who directs the Lord's Church on the Earth.
How can we know if a man is a Prophet from God?
By Praying to our Heavenly Father and asking for a Spiritual Witness that the Prophet in question is truly God's chosen representative. We can also read the Scriptures to understand the Gospel and receive Spiritual impressions as they have been written by past Prophets and Apostles.
So why did all the Prophets go away?
Throughout history, God has chosen prophets, such as Noah, Abraham, Moses, and others, to teach the gospel and direct His Church (Amos 3:7). It is no different today. We all need God’s guidance in a world that is sometimes confusing. Because God loves His children, He continues to send living prophets. Joseph Smith (1805–1844) was the first prophet of our time. Thomas S. Monson is God’s chosen prophet today.