Objection 1. It would seem that it was unbecoming that the Magi should come to adore Christ and pay homage to Him. For reverence is due to a king from his subjects. But the Magi did not belong to the kingdom of the Jews. Therefore, since they knew by seeing the star that He that was born was the "King of the Jews," it seems unbecoming that they should come to adore Him.
Objection 2. Further, it seems absurd during the reign of one king to proclaim a stranger. But in Judea Herod was reigning. Therefore it was foolish of the Magi to proclaim the birth of a king.
Objection 3. Further, a heavenly sign is more certain than a human sign. But the Magi had come to Judea from the east, under the guidance of a heavenly sign. Therefore it was foolish of them to seek human guidance besides that of the star, saying: "Where is He that is born King of the Jews?"
Objection 4. Further, the offering of gifts and the homage of adoration are not due save to kings already reigning. But the Magi did not find Christ resplendent with kingly grandeur. Therefore it was unbecoming for them to offer Him gifts and homage.
On the contrary, It is written (Isaiah 60:3): "[The Gentiles] shall walk in the light, and kings in the brightness of thy rising." But those who walk in the Divine light do not err. Therefore the Magi were right in offering homage to Christ.
I answer that, As stated above (3, ad 1), the Magi are the "first-fruits of the Gentiles" that believed in Christ; because their faith was a presage of the faith and devotion of the nations who were to come to Christ from afar. And therefore, as the devotion and faith of the nations is without any error through the inspiration of the Holy Ghost, so also we must believe that the Magi, inspired by the Holy Ghost, did wisely in paying homage to Christ.
Reply to Objection 1. As Augustine says in a sermon on the Epiphany (cc.): "Though many kings of the Jews had been born and died, none of them did the Magi seek to adore. And so they who came from a distant foreign land to a kingdom that was entirely strange to them, had no idea of showing such great homage to such a king as the Jews were wont to have. But they had learnt that such a King was born that by adoring Him they might be sure of obtaining from Him the salvation which is of God."
Reply to Objection 2. By proclaiming [Christ King] the Magi foreshadowed the constancy of the Gentiles in confessing Christ even until death. Whence Chrysostom says (Hom. ii in Matth.) that, while they thought of the King who was to come, the Magi feared not the king who was actually present. They had not yet seen Christ, and they were already prepared to die for Him.
Reply to Objection 3. As Augustine says in a sermon on the Epiphany (cc.): "The star which led the Magi to the place where the Divine Infant was with His Virgin-Mother could bring them to the town of Bethlehem, in which Christ was born. Yet it hid itself until the Jews also bore testimony of the city in which Christ was to be born: so that, being encouraged by a twofold witness," as Pope Leo says (Serm. xxxiv), "they might seek with more ardent faith Him, whom both the brightness of the star and the authority of prophecy revealed." Thus they "proclaim" that Christ is born, and "inquire where; they believe and ask, as it were, betokening those who walk by faith and desire to see," as Augustine says in a sermon on the Epiphany (cxcix). But the Jews, by indicating to them the place of Christ's birth, "are like the carpenters who built the Ark of Noah, who provided others with the means of escape, and themselves perished in the flood. Those who asked, heard and went their way: the teachers spoke and stayed where they were; like the milestones that point out the way but walk not" (Augustine, Serm. cclxxiii). It was also by God's will that, when they no longer saw the star, the Magi, by human instinct, went to Jerusalem, to seek in the royal city the new-born King, in order that Christ's birth might be publicly proclaimed first in Jerusalem, according to Isaiah 2:3: "The Law shall come forth from Sion, and the Word of the Lord from Jerusalem"; and also "in order that by the zeal of the Magi who came from afar, the indolence of the Jews who lived near at hand, might be proved worthy of condemnation" (Remig., Hom. in Matth. ii, 1).
Reply to Objection 4. As Chrysostom says (Hom. ii in Matth. [From the supposititious Opus Imperfectum): "If the Magi had come in search of an earthly King, they would have been disconcerted at finding that they had taken the trouble to come such a long way for nothing. Consequently they would have neither adored nor offered gifts. But since they sought a heavenly King, though they found in Him no signs of royal pre-eminence, yet, content with the testimony of the star alone, they adored: for they saw a man, and they acknowledged a God." Moreover, they offer gifts in keeping with Christ's greatness: "gold, as to the great King; they offer up incense as to God, because it is used in the Divine Sacrifice; and myrrh, which is used in embalming the bodies of the dead, is offered as to Him who is to die for the salvation of all" (Gregory, Hom. x in Evang.). And hereby, as Gregory says (Hom. x in Evang.), we are taught to offer gold, "which signifies wisdom, to the new-born King, by the luster of our wisdom in His sight." We offer God incense, "which signifies fervor in prayer, if our constant prayers mount up to God with an odor of sweetness"; and we offer myrrh, "which signifies mortification of the flesh, if we mortify the ill-deeds of the flesh by refraining from them."
Source: Summa Theologica (New Advent)