Throughout history God has called prophets. There has also been many instances of apostasy. Apostasy is when people choose to reject the prophets and their teaching. When people chose to reject the prophets, God would withdraw His priesthood authority from the earth. When the time was right, God would call another prophet to restore His gospel anew. God even sent His Son, Jesus Christ. Incredibly, people even rejected and crucified Him. With the death of Christ and the rejection of His Apostles, the world fell into a dark night of apostasy.
God loves us so much that when the time was right, He again reached out to His children in love. After the long night of darkness and apostasy, God called another prophet to restore His gospel anew! This prophet is Joseph Smith!