38 Again, how clear is the declaration made by God the Father through Isaiah concerning our Lord! He says, For thus says the Lord, the holy God of Israel, Who made the things to come, Ask me concerning your sons and your daughters, and concerning the works of My hands command ye Me. I have made the earth and man upon it, I have commanded all the stars, I have raised up a King with righteousness, and all His ways are straight. He shall build My city, and shall turn back the captivity of My people, not for price nor reward, says the Lord of Sabaoth.
Egypt shall labour, and the merchandise of the Ethiopians and Sabeans. Men of stature shall come over unto You and shall be Your servants, and shall follow after You, bound in chains, and shall worship You and make supplication unto You, for God is in You and there is no God beside You. For You are God, and we knew it not, O God of Israel, the Saviour. All that resist Him shall be ashamed and confounded, and shall walk in confusion. Is any opening left for gainsaying, or excuse for ignorance?
If blasphemy continue, is it not in brazen defiance that it survives? God from Whom are all things, Who made all by His command, asserts that He is the Author of the universe, for, unless He had spoken, nothing had been created. He asserts that He has raised up a righteous King, who builds for Himself, that is, for God, a city, and turns back the captivity of His people, for no gift nor reward, for freely are we all saved. Next, He tells how after the labours of Egypt, and after the traffic of Ethiopians and Sabeans, men of stature shall come over to Him.
How shall we understand these labours in Egypt, this traffic of Ethiopians and Sabeans? Let us call to mind how the Magi of the East worshipped and paid tribute to the Lord; let us estimate the weariness of that long pilgrimage to Bethlehem of Judah. In the toilsome journey of the Magian princes we see the labours of Egypt to which the prophet alludes. For when the Magi executed, in their spurious, material way, the duty ordained for them by the power of God, the whole heathen world was offering in their person the deepest reverence of which its worship was capable.
And these same Magi presented gifts of gold and frankincense and myrrh from the merchandise of the Ethiopians and Sabeans; a thing foretold by another prophet, who has said, The Ethiopians shall fall down before His face, and His enemies shall lick the dust. The Kings of Tharsis shall offer presents, the Kings of the Arabians and Sabeans shall bring gifts, and there shall be given to Him of the gold of Arabia. The Magi and their offerings stand for the labour of Egypt and for the merchandise of Ethiopians and Sabeans; the adoring Magi represent the heathen world, and offer the choicest gifts of the Gentiles to the Lord Whom they adore.
Source: On the Trinity (New Advent)