If John’s baptism was a “baptism of repentance for the forgiveness of sins” (Lk 3:3), why was Jesus baptized? The Evangelists depict Jesus as the one who calls others to repentance (Mk 1:15) and forgives sin (Mk 2:5) but nowhere do they suggest that Jesus repented for His sins. In fact, in John’s Gospel, John declares that Jesus is “the Lamb of God who takes away the sins of the world” (Jn 1:29).
Why Jesus was baptized has to be seen in the context of how John and Jesus understood John’s baptism. The early Christian tradition clearly saw John in relation to Christ. The fact that the Synoptics depict John as baptizing Jesus could easily suggest that John was superior to Jesus. The Evangelists might have been more hesitant to include the account of the baptism, especially since the Acts of the Apostles lets us know that disciples of John continued into early Christian times, even as far as Ephesus (Acts 18:25, 19:3).
Why was Jesus’ baptism so important that the Evangelists considered it a necessary part of the story? The Acts of the Apostles traces the beginning of Jesus’ ministry to the baptism of John: “… how Jesus of Nazareth began in Galilee, after John had been preaching baptism” (Acts 10:37).
The Gospels and the Acts see John’s role as preparatory to Jesus. The Gospel of John affirms: “That He may be manifest in Israel, I came baptizing with water” (Jn 1:31). Similarly, in Matthew, “the one who comes after me is more powerful than I” (Mt 3:11; cf. Mk 3:6, Lk 3:16)
Following the understanding of the Gospels, St. Thomas Aquinas maintains: “The whole teaching and work of John was in preparation for Christ” (3a. 38, 2, ad 2). According to Thomas, John’s baptism was a sign of an intention to reform but in itself it did not effect a change: “Neither did they receive anything, save only the sign of penance” (3a. 38, 4 ad 2).
In the Gospel tradition, John connected the Holy Spirit with Jesus’ baptism. In Matthew’s and Mark’s Gospels, John announces, “I baptize you in water, but… He shall baptize you in the Holy Spirit” (Mt 3:11; Mk 1:8). The Gospel of Luke asserts: “He will baptize you with the Holy Spirit and fire” (Lk 3:6). In the Gospel of John, John is told: “The man on whom you see the Spirit come down and rest is the one who is to baptize with the Holy Spirit” (Jn 1:33).
Thomas comments, “By the baptism of the New Law men are baptized inwardly by the Holy Spirit, and this is accomplished by God alone” (3a. 38, 3 ad 1). Thomas recalls Augustine’s words, “our sacraments are signs of present grace” (3a. 38, 6 ad 5; Augustine, Contra Faustus, 19).
If Jesus did not need to repent and the baptism that He will bring is superior to that of John, why did Jesus approach John to be baptized? Thomas follows the idea of some of the Fathers that Jesus was baptized to draw us to baptism: “Christ wished to be baptized in order by His example to lead us to baptism… that He might lead us more efficaciously, He wished to be baptized…” (3a. 39, 2, ad 1).
Thomas recalls the words of Ambrose that justice consists in doing first what you wish others to do and so you “encourage others by your example” (3a. 39, 1, ad 2; Ambrose, Commentary on Luke’s Gospel, 3, 21). The fact that Jesus underwent an exterior rite verifies that, interiorly, we encounter Christ and His grace in the exterior rites of the sacraments.
Thomas picks up on the words of the Fathers of the Church that Jesus was baptized, “that He might sanctify baptism” (3a. 38, 1) and “in order to consecrate the baptism with which we were to be baptized” (3a. 39, 5). Thomas recalls that Ambrose had said that by His Baptism, Christ cleansed the water by the flesh of Christ that knew no sin (3a. 39, 1; Ambrose, Commentary on Luke’s Gospel, 3, 21).
We might not see the connection immediately. However, Thomas affirms: “We become receivers of this grace through God’s Son made man, whose humanity grace first filled, and then flowed to us” (1a2ae. 108, 1). By undergoing Baptism, Jesus made baptism a means of grace for us.
Thomas relates Jesus’ baptism to the effects of our own baptisms. Just as the heavens opened when Christ was baptized, in baptism, the heavens are opened for us: “Those who are baptized make a profession of faith, and baptism is called the ‘sacrament of faith.’ Now by faith we gaze on heavenly things, which surpass the senses and human reason” (3a. 39, 5).
Thomas notices that Luke says, “Jesus, having been baptized and was praying, the heavens opened” (Lk 3:21). Thomas reflects “… the very fact that through baptism heaven is opened to believers is in virtue of the prayer of Christ” (3a. 39, 5).
Thomas instructs that Christ’s Passion opens heaven in general but heaven is open to each one in baptism: “Christ’s Passion is the common cause of the opening of heaven to me. But it behooves this cause to be applied to each one, in order that he enter heaven. And this is effected by baptism: ‘All who are baptize in Christ Jesus are baptized in His death’” (3a. 39, 6 ad 3). Thomas notes “At Christ’s baptism the heavens were opened as though the way had been shown by which we were to enter into heaven” (3a. 39, 5, ad 3)
Thomas calls attention to the Trinitarian aspects of the Baptism: “For the Son was in the flesh, the Father in the voice and the Holy Spirit in the form of a dove” (Commentary on Matthew).
The Spirit descended on Jesus but also on us: “All those who are baptized with the baptism of Christ receive the Holy Spirit… Therefore it was fitting that he Holy Spirit should descend upon Him” (3a. 39, 6).
Baptism makes us God’s children in the Son: “… especially at the time of baptism, by which men are born again into adopted sons of God, since God’s sons by adoption are made to be like His natural Son: ‘Whom He foreknew, He also predestined to be conformable to the image of His Son’ (Rom 8:29)” (3a. 39, 8 ad 3).
Thomas compares the Father’s love for those whom He has created with the delight of an artist in his or her work: “For in whatever one's good is reflected, in it something is pleased with it, as an artisan takes pleasure in his beautiful work of art, and as a man in his beautiful image reflected in a mirror. The divine goodness is in every individual creature” (Commentary on Matthew)
However, this resemblance is “never as whole and perfect except in the Son and the Holy Spirit.” Therefore the Father is “totally pleased in the Son, who has as much goodness as the Father.” (Commentary on Matthew). "The Father loves the Son, and has given all things in his hands" (Jn 3:55).
Denis Vincent Wiseman, O.P.
The translations from the Commentary on the Gospel of St. Matthew were done by Fabian Larcher, O.P. The full text is available on the web page of the Dominican House of Studies in Washington DC: http://dhspriory.org/thomas/
 References to St. Thomas’ Summa Theologiae customarily give the part of the Summa, the question and the article. In this case, the reference is to the third part of the Summa. An “a” follows the 3 because the Latin for the third part is Tertia. The question is 38, “On the Baptism of John,” and the article is the second, “Whether the Baptism of John was from God?” In the beginning of each article, Thomas raises objections to what he will explain. After he has given his answer, he replies to the objections. This is his reply to the second objection, which is identified with the Latin preposition, ad, meaning “to.”