Remember that John the Baptist did not want to baptize the Savior. He considered himself unworthy and understood that the ordinance was designed for the wicked. It was only at the insistence of the Savior that he acquiesced.
' Then cometh Jesus from Galilee to Jordan unto John, to be baptized of him.
But John forbad him, saying, I have need to be baptized of thee, and comest thou to me?
And Jesus answering said unto him, Suffer it to be so now: for thus it becometh us to fulfil all righteousness. Then he suffered him.' (Matt 3:13-15)
"Though Jesus was God; though He reigned in the heavenly kingdom; though He was alive spiritually and fit in all respects to return to the presence of the Father - yet He was baptized. He was baptized in order to gain salvation in the celestial kingdom of God, thereby setting the perfect example for all men." (Church News, "Jesus, the Sinless One, Was Baptized by John to Fulfill All", Jan. 14, 1995, p. 21)
"Nephi, to dramatize the importance of baptism, tells us that the Savior had to be baptized to "fulfill all righteousness" (2 Nephi 31:5). The doctrine is both little understood and marvelously important. In the high spiritual sense there is no righteousness without willing submission to all the ordinances of salvation. No more perfect example could be found than Christ himself. Christ, who was sinless, had to be baptized in order to be considered righteous. To be righteous, as the word is used in its highest spiritual sense, means far more than being sinless, pure, or merely good. Righteousness is not simply the absence of evil or impropriety; it is the active seeking of the mind and will of the Father and compliance with that will once it has been obtained." (McConkie and Millet, Doctrinal Commentary on the Book of Mormon, vol. 1, p. 361)
Bruce R. McConkie
"Nephi explains that Christ did fulfil all righteousness in being baptized in that: 1. He humbled himself before the Father; 2. He covenanted to be obedient and keep the Father's commandment; 3. He had to be baptized to gain admission to the celestial kingdom; and 4. He set an example for all men to follow. (2 Ne. 31:4-11.) Our Lord's baptism 'showeth unto the children of men the straightness of the path, and the narrowness of the gate, by which they should enter, he having set the example before them.' (2 Ne. 31:9.) If even the King of the kingdom could not return to his high state of pre-existent exaltation without complying with his own eternal law for admission to that kingdom, how can any man expect a celestial inheritance without an authorized and approved baptism?" (Mormon Doctrine, p. 71)