Reply Obj. 2: In baptism we "go up" by advancing in grace: for which we need to "go down" by humility, according to James 4:6: "He giveth grace to the humble." And to this "going down" must the name of the Jordan be referred.
Reply Obj. 3: As Augustine says in a sermon for the Epiphany (x): "As of yore the waters of the Jordan were held back, so now, when Christ was baptized, the torrent of sin was held back." Or else this may signify that against the downward flow of the waters the river of blessings flowed upwards. _______________________
FIFTH ARTICLE [III, Q. 39, Art. 5]
Whether the Heavens Should Have Been Opened Unto Christ at His
Baptism?
Objection 1: It would seem that the heavens should not have been opened unto Christ at His baptism. For the heavens should be opened unto one who needs to enter heaven, by reason of his being out of heaven. But Christ was always in heaven, according to John 3:13: "The Son of Man who is in heaven." Therefore it seems that the heavens should not have been opened unto Him.
Obj. 2: Further, the opening of the heavens is understood either in a corporal or in a spiritual sense. But it cannot be understood in a corporal sense: because the heavenly bodies are impassible and indissoluble, according to Job 37:18: "Thou perhaps hast made the heavens with Him, which are most strong, as if they were of molten brass." In like manner neither can it be understood in a spiritual sense, because the heavens were not previously closed to the eyes of the Son of God. Therefore it seems unbecoming to say that when Christ was baptized "the heavens were opened."
Obj. 3: Further, heaven was opened to the faithful through Christ's Passion, according to Heb. 10:19: "We have [Vulg.: 'Having'] a confidence in the entering into the holies by the blood of Christ." Wherefore not even those who were baptized with Christ's baptism, and died before His Passion, could enter heaven. Therefore the heavens should have been opened when Christ was suffering rather than when He was baptized.
On the contrary, It is written (Luke 3:21): "Jesus being baptized and praying, heaven was opened."
I answer that, As stated above (A. 1; Q. 38, A. 1), Christ wished to be baptized in order to consecrate the baptism wherewith we were to be baptized. And therefore it behooved those things to be shown forth which belong to the efficacy of our baptism: concerning which efficacy three points are to be considered. First, the principal power from which it is derived; and this, indeed, is a heavenly power. For which reason, when Christ was baptized, heaven was opened, to show that in future the heavenly power would sanctify baptism.
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.