God's Heavenly Messengers

The Prophecy of John the Baptist in the Old Testament (accepted by some sources of in-depth Biblical studies)

There are several passages within the Old Testament which are interpreted by Christians as being prophetic of John the Baptist in this role. These include a passage in the Book of Malachi 3:1 that refers to a prophet who would prepare the way of the Lord:
"Behold, I will send my messenger, and he shall prepare the way before me: and the Lord, whom ye seek, shall suddenly come to his temple, even the messenger of the covenant, whom ye delight in: behold, he shall come, saith the LORD of hosts. — Malachi 3:1 
(sourse: Wikipedia)

Note: John the Baptist and not John the Apostle (John the Revelator, author of the book of 'Revelation' {or the book of the Apocalypse in some Bible tranlations/Spanish}) was related to Jesus. John the Baptist was the son of Zechariah and Elizabeth (Luke 1:5-25). Jesus was Mary's son, conceived through the power of the Holy Spirit (Luke 1:26-38). Mary was Elizabeth's cousin (Luke 1:36). So the relation between Jesus and John the Baptist was that of second cousins.