Matthew 3

As John the Baptist preached in the wilderness of Judaea -

"Then went out to him Jerusalem, and all Judæa, and all the region round about Jordan,
6 And were baptized of him in Jordan, confessing their sins."  (New Testament | Matthew 3:5 - 6)

This seems apparent to me that repentance and baptism had always been had throughout the Old Testament, but may have been downplayed as arrogant religious leaders considered their heritage to be of greater value, for as John -

"...saw many of the Pharisees and Sadducees come to his baptism, he said unto them, O generation of vipers, who hath warned you to flee from the wrath to come?
8 Bring forth therefore fruits meet for repentance:
9 And think not to say within yourselves, We have Abraham to our father: for I say unto you, that God is able of these stones to raise up children unto Abraham."  (New Testament | Matthew 3:7 - 9)

Obviously, the Jewish leaders had evolved from humility and repentance to an inherent right of salvation as he taught -

"...now also the axe is laid unto the root of the trees: therefore every tree which bringeth not forth good fruit is hewn down, and cast into the fire."  (New Testament | Matthew 3:10)

As the old was about to be replaced by the new, John prepared the way as he taught some true basics of the doctrine of Christ...that of faith, repentance, baptism by immersion and an obligation of bringing for good works throughout their lives.