Do we know why Jesus was baptized at the age of 30 and not earlier in life?
Nephi explains to us that there are four reasons why Jesus was baptized. First He was baptized to “fulfill all righteousness.” Second His baptism showed “He humbleth Himself… and witnesseth unto the Father that He would be obedient…in keeping all of the commandments.” Third His baptism shows the “straitness of the path, and narrowness of the gate, by which they should enter.” Fourth His baptism set the example for us to follow. (2 Ne. 31: 5-10) His baptism was not for the remission of sins, as He was without sin.
In order to recognize why Jesus was baptized when he was 30, we need to turn our attention to the man that baptized Him. John the Baptist’s mission was foretold as early as with Isaiah approximately 700 B.C. (Isa. 40:3). His mission was to “Prepare ye the way of the Lord” and to baptize the Savior. He was ordained and given this authority by an angel when he was eight days old. His father, Zacharias, held the Aaronic Priesthood, but did not hold the keys that John needed. President Joseph Fielding Smith explained the ordination of John as follows: “The reason Zacharias could not ordain John is because of the fact that John received certain keys of authority which his father did not possess. Therefore this special authority had to be conferred by this heavenly messenger, who was duly authorized and sent to confer it. John’s ordination was not merely the bestowal of the Aaronic Priesthood, which his father held, but also the conferring of certain essential powers peculiar to the time among which was the authority to overthrow the kingdom of the Jews and “to make straight the way of the Lord.’ Moreover, it was to prepare the Jews and other Israelites for the coming of the Son of God. This great authority required a special ordination beyond the delegated power that had been given to Zacharias or any other priest who went before him, so the angel of the Lord was sent to John in his childhood to confer it.” Answers to Gospel Questions, vol. 5, p. 2.
John was told that he would recognize the Savior when He baptized Him. We read in John 1: 32″ And John bare record, saying, I saw the Spirit descending from heaven like a dove, and it abode upon him. 33 And I knew him not: but he that sent me to baptize with water, the same said unto me, Upon whom thou shalt see the Spirit descending, and remaining on him, the same is he which baptizeth with the Holy Ghost. 34 And I saw, and bare record that this is the Son of God.”
John, as with Jesus, did not start His ministry until He was 30. This being the Jewish law and custom John was six months older than Jesus and as such was able to prepare the people for one who was “preferred before me, whose shoe’s latchet I am not worthy to unloose.” (John 1: 27) He also fulfilled the second part of his mission, to baptise the Savior.