Today we celebrate the Feast of the Baptism of our Lord by St. John the Baptist. The meaning behind Christ's baptism is of perennial interest, since He had neither sin to repent of nor anything to be cleansed of; Christ Himself says that He submits to baptism to “fulfill all righteousness” (Matt. 3:15), but what does this phrase mean exactly? There are several reasons why Jesus consented to a baptism that, as John the Baptist noted, He did not need. I have put together the four most commonly given reasons, from the Fathers and the Magisterium of the Church.
First, according to the Catechism, it is a manifestation of His self-emptying and identification with humanity, which stands in need of God’s grace and forgiveness (CCC 1224). In doing so, he shows what we are to do. Similarly, he was circumcised according to the precepts of the Mosaic Law, even though circumcision symbolized a cutting off of sin, which Jesus did not have. St. Thomas Aquinas makes this same point: "It was fitting that Christ should not only fulfill what was prescribed by the Old Law, but also begin what appertained to the New Law. Therefore He wished not only to be circumcised, but also to be baptized" (STh III.Q. 39 Art. 1), and Augustine, "because He wished to do what He had commanded all to do" (Sermo cxxxvi). This is what He meant by "to fulfill all righteousness."
Second, we could see Christ's baptism as the formal inauguration of His messianic mission, wherein He is anointed by the Spirit for His ministry (Luke 4:16-20). This is how the event is portrayed in the Gospels.The Catechism (536) says: "The baptism of Jesus is on his part the acceptance and inauguration of his mission as God's suffering Servant. He allows himself to be numbered among sinners; he is already "the Lamb of God, who takes away the sin of the world". Already he is anticipating the "baptism" of his bloody death. Already he is coming to "fulfill all righteousness", that is, he is submitting himself entirely to his Father's will: out of love he consents to this baptism of death for the remission of our sins. The Father's voice responds to the Son's acceptance, proclaiming his entire delight in his Son.The Spirit whom Jesus possessed in fullness from his conception comes to "rest on him". Jesus will be the source of the Spirit for all mankind. At his baptism "the heavens were opened" - the heavens that Adam's sin had closed - and the waters were sanctified by the descent of Jesus and the Spirit, a prelude to the new creation."
Third, by His baptism, Christ sacramentally sanctifies the waters for us, prefiguring the baptism He was to later inaugurate. Here is the way this works; consider leprosy: Anyone who came in contact with a leper contracted the leper's uncleanliness; but Christ, rather than contracting uncleanliness, transfers His own divine cleanliness to the lepers upon contact with them. Similarly, instead of being made unclean by touching a dead body, the dead body is made alive by contact with Christ. This case applies to water as well; instead of the water purifying Christ, it is Christ who purifies the water. This theme of Christ sanctifying the waters is present in many of the writings of the Fathers as well. Consider:
St. Ignatius of Antioch: "For our God, Jesus the Christ, was conceived by Mary by the dispensation of God, as well as of the seed of David as of the Holy Spirit: he was born, and was baptized, that by himself submitting he might purify the water (Letter to the Ephesians, 18).
St. Gregory of Nyssa: "[In] the birth by water and the Spirit, Jesus himself led the way in this birth, drawing down upon the water, by his own baptism, the Holy Spirit; so that in all things he became the firstborn of those who are spiritually born again, and gave the name of brethren to those who partook in a birth like to his own by water and the Spirit" (Against Eunomius 2:8, c. 382).
St. Ambrose of Milan: "The Lord was baptized, not to be cleansed himself but to cleanse the waters, so that those waters, cleansed by the flesh of Christ which knew no sin, might have the power of baptism. Whoever comes, therefore, to the washing of Christ lays aside his sins" (Commentary on Luke 2:83, A.D. 389).
St. Maximus of Turin: "Someone might ask, "Why would a holy man desire baptism?" Listen to the answer: Christ is baptized, not to be made holy by the water, but to make the water holy, and by his cleansing to purify the waters which he touched. For the consecration of Christ involves a more significant consecration of the water. For when the Savior is washed all water for our baptism is made clean, purified at its source for the dispensing of baptismal grace to the people of future ages. Christ is the first to be baptized, then, so that Christians will follow after him with confidence" (Sermon on the Feast of the Epiphany, c. 430)
Finally, we could say that Christ's baptism mystically reveals what occurs spiritually every time a Christian is baptized. When we come to the Holy Font, the heavens are opened, the Spirit descends, and the Father pronounces, “You are my beloved son.” St. Aphrahaat says, "From baptism we receive the Spirit of Christ. At that same moment in which the priests invoke the Spirit, heaven opens, and he descends and rests upon the waters, and those who are baptized are clothed in him” (Treatises 6:14:4, A.D. 340).St. Hilary of Poitiers says: "Everything that happened to Christ lets us know that, after the bath of water, the Holy Spirit swoops down upon us from high heaven and that, adopted by the Father's voice, we become sons of God" (In Matth. 2,5, c. 360).
In conclusion, let us quote from St. Thomas Aquinas (III.39.1), who wraps up all of these reasons in a single, concise answer:
"I answer that, it was fitting for Christ to be baptized. First, because, as Ambrose says on Luke 3:21: "Our Lord was baptized because He wished, not to be cleansed, but to cleanse the waters, that, being purified by the flesh of Christ that knew no sin, they might have the virtue of baptism"; and, as Chrysostom says (Hom. iv in Matth.), "that He might bequeath the sanctified waters to those who were to be baptized afterwards." Secondly, as Chrysostom says (Hom. iv in Matth.), "although Christ was not a sinner, yet did He take a sinful nature and 'the likeness of sinful flesh.' Wherefore, though He needed not baptism for His own sake, yet carnal nature in others had need thereof." And, as Gregory Nazianzen says (Orat. xxxix) "Christ was baptized that He might plunge the old Adam entirely in the water." Thirdly, He wished to be baptized, as Augustine says in a sermon on the Epiphany (cxxxvi), "because He wished to do what He had commanded all to do." And this is what He means by saying: "So it becometh us to fulfill all justice" (Matthew 3:15). For, as Ambrose says (on Luke 3:21), "this is justice, to do first thyself that which thou wishest another to do, and so encourage others by thy example."