Thomas Aquinas

“ Secondly, the faith of the Church and of the person baptized conduces to the efficacy of baptism: wherefore 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. And in order to signify this, the heavens were opened when Christ was baptized. ”

“ Thirdly, because by Christ's being baptized at the perfect age, we are given to understand that baptism brings forth perfect men, according to Eph. 4:13: "Until we all meet into the unity of faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the age of the fulness of Christ." ”

“ To faith, because in this manner His human nature is shown to be real, by its making bodily progress with the advance of time; and lest this progress should be deemed imaginary, He did not wish to show His wisdom and power before His body had reached the perfect age: to humility, lest anyone should presume to govern or teach others before attaining to perfect age. ”

“ It would seem that it is not fitting to say that when Christ was baptized the Holy Ghost came down on Him in the form of a dove. For the Holy Ghost dwells in man by grace. But the fulness of grace was in the Man-Christ from the beginning of His conception, because He was the "Only-begotten of the Father," as is clear from what has been said above ( [4203] Q [7] , A [12] ; [4204] Q [34] , A [1] ) . Therefore the Holy Ghost should not have been sent to Him at His baptism. ”

“ Thirdly, because the entrance to the heavenly kingdom was opened to us by the baptism of Christ in a special manner, which entrance had been closed to the first man through sin. Hence, when Christ was baptized, the heavens were opened, to show that the way to heaven is open to the baptized.
Now after baptism man needs to pray continually, in order to enter heaven: for though sins are remitted through baptism, there still remain the fomes of sin assailing us from within, and the world and the devils assailing us from without. ”

“ But no small danger besets any other man who departs from this life without being clothed with the garment of incorruptibility"---namely, grace. And though it be a good thing to remain clean after baptism, "yet is it still better," as he says, "to be slightly sullied now and then than to be altogether deprived of grace."
Reply to Objection 2: The profit which accrues to men from Christ is chiefly through faith and humility: to both of which He conduced by beginning to teach not in His boyhood or youth, but at the perfect age. ”

“ Christ's Passion is the common cause of the opening of heaven to men. But it behooves this cause to be applied to each one, in order that he enter heaven. And this is effected by baptism, according to Rom. 6:3: "All we who are baptized in Christ Jesus are baptized in His death." Wherefore mention is made of the opening of the heavens at His baptism rather than at His Passion. ”

“ For the reality should correspond to the figure. But baptism was prefigured in the crossing of the Red Sea, where the Egyptians were drowned, just as our sins are blotted out in baptism. Therefore it seems that Christ should rather have been baptized in the sea than in the river Jordan.
Objection 2: Further, "Jordan" is interpreted a "going down." But by baptism a man goes up rather than down: wherefore it is written (Mat. 3:16) that "Jesus being baptized, forthwith came up [Douay: 'out'] from the water." Therefore it seems unfitting that Christ should be baptized in the Jordan. ”

“ Again, the dove prefers the more choice seeds. This refers to the gift of knowledge, whereby the saints make choice of sound doctrines, with which they nourish themselves. Further, the dove feeds the brood of other birds. This refers to the gift of counsel, with which the saints, by teaching and example, feed men who have been the brood, i.e. imitators, of the devil. Again, the dove tears not with its beak. This refers to the gift of understanding, wherewith the saints do not rend sound doctrines, as heretics do. Again, the dove has no gall. ”

“ Christ was set before men as an example to all. Wherefore it behooved that to be shown forth in Him, which is becoming to all according to the common law---namely, that He should teach after reaching the perfect age. ”

“ It can also be referred to the imaginary vision, in which manner Ezechiel saw the heavens opened: since such a vision was formed in Christ's imagination by the Divine power and by His rational will, so as to signify that the entrance to heaven is opened to men through baptism. Lastly, it can be referred to intellectual vision: forasmuch as Christ, when He had sanctified baptism, saw that heaven was opened to men: nevertheless He had seen before that this would be accomplished. ”

“ But, as Gregory Nazianzen says (Orat. xxxix) , that which seldom occurs is not the law of the Church; as "neither does one swallow make the spring." For by special dispensation, in accordance with the ruling of Divine wisdom, it has been granted to some, contrary to the common law, to exercise the functions of governing or teaching. ”

“ Thirdly, as Gregory Nazianzen says (Orat. xxxix) , "by going to John to be baptized by him, He sanctified baptism."
Reply to Objection 1: As stated above [4201] (A [1] ) , Christ wished to be baptized in order by His example to lead us to baptism. And so, in order that He might lead us thereto more efficaciously, He wished to be baptized with a baptism which He clearly needed not, that men who needed it might approach unto it. Wherefore Ambrose says on Lk. 3:21: "Let none decline the laver of grace, since Christ did not refuse the laver of penance." ”