John the Baptist prepared the way for Jesus Christ to come

Ancient forerunners ran before the chariot of the King, cleared rocks and other obstacles from his path, and loudly proclaimed his coming. Similarly, John prepared for the coming of Jesus Christ. He exposed the false teaching and sins of the leaders, preached repentance, and proclaimed the imminent coming of the Messiah. His influence extended to individuals who later became followers of the Savior. Andrew followed John's teachings and Peter was his brother. John the Beloved may also have been a disciple of John the Baptist. And Peter suggests in
Acts that others of the Twelve were tutored by John (see http://beardall2000.com/nt/nt04.html).

The prophet Joseph Smith summarized the role of John the Baptist. First, he was entrusted with the divine role of preparing for the coming of the Savior. Second, he was required to baptize the Lord and testify of his divinity. Finally, he was the only legitimate authority at that time on earth. Christ recognized this and came to him to be baptized (TPJS, p. 276).

A similar command is given to us in D&C 65 which is a prayer given through Joseph Smith. We also are to prepare for the coming of Christ. (see http://scriptures.lds.org/en/dc/65)

The Aaronic Priesthood, which John restored to Joseph Smith and Oliver Cowdery, is a preparatory priesthood. It prepares someone to receive the Melchizedek Priesthood. It also plays a key role in preparing for the coming of Christ. (see http://scriptures.lds.org/en/dc/13)