II. The wise men from the East are typical fulfilments of God's promise to Abraham
Now the manifestation of this unspeakable mercy, dearly-beloved, came to pass when Herod held the royal power in Judea, where the legitimate succession of Kings having failed and the power of the High-priests having been overthrown, an alien-born had gained the sovereignty: that the rising of the true King might be attested by the voice of prophecy, which had said: “a prince shall not fail from Juda, nor a leader from his loins, until He come for whom it is reserved, and He shall be the expectation of the nations.”
Concerning which an innumerable succession was once promised to the most blessed patriarch Abraham to be begotten not by fleshly seed but by fertile faith; and therefore it was compared to the stars in multitude that as father of all the nations he might hope not for an earthly but for a heavenly progeny. And therefore, for the creating of the promised posterity, the heirs designated under the figure of the stars are awakened by the rising of a new star, that the ministrations of the heaven might do service in that wherein the witness of the heaven had been adduced.
A star more brilliant than the other stars arouses wise men that dwell in the far East, and from the brightness of the wondrous light these men, not unskilled in observing such things, appreciate the importance of the sign: this doubtless being brought about in their hearts by Divine inspiration, in order that the mystery of so great a sight might not be hid from them, and, what was an unusual appearance to their eyes, might not be obscure to their minds. In a word they scrupulously set about their duty and provide themselves with such gifts that in worshipping the One they may at the same time show their belief in His threefold function: with gold they honour the Person of a King, with myrrh that of Man, with incense that of God.
Source: Sermons (New Advent)