Luke 1:18

And Zacharias said to the angel, &c. That is, give a sign or a miracle for a proof to me that the great things which you are promising will surely come to pass. This hesitation on the part of Zacharias seems to have proceeded from want of deliberation and reflection, and therefore was only a venial sin, for which he was punished by being deprived of the power of speech. For otherwise did Abraham, who, when the angel promised that Isaac should be born to him from Sarah who was barren, immediately believed, "for he was strong in faith, giving glory to God, being fully persuaded that what He had promised, He was able also to perform," Romans 4:20-21.

Ver. 19. I am Gabriel, who stand. That is, "I am wont to stand, ready to minister to the will of God in all things; I am not indeed now standing before Him in heaven, for I have been sent thence to thee to the earth." Although on the earth angels may also stand before God, and behold His Face; for God is everywhere (S. Matt. xviii. 10). Hence we may gather that the same angels stand before God and minister to Him, although S. Dionysius the Areopagite and S. Gregory deny this; for Gabriel stands before God and ministers to Him, and is sent to Zacharias.

Moreover, the words "stand before" signify that Gabriel is one of the seven angels who are the chiefs of the heavenly court, as are also Michael and Raphael (Tobit 12:15). Of these seven angels I have spoken at length on Apocal. i. 4. Wherefore although some, as Toletus, are of opinion that Gabriel belongs to the last order but one, which is that of archangels, because he is elsewhere called an archangel, yet he more truly seems to be one of the first order which is that of seraphim, and therefore is called by many an archangel; and there are not wanting some who think that he is the first of all among the seraphim. Cardinal Vignerius (in Decachordo Christ. Cord i. 2) proves this by eight reasons which I have enumerated on Daniel 9:21. All of which are reduced to this one. For the highest work it is fitting that the highest angel should be sent; but the Incarnation of the Word is the highest work of God, therefore Gabriel, who was sent to announce that, is the highest angel. But this reason is not conclusive, as I have there shown. For the common opinion of theologians is that Michael is the highest of all the angels, and the Antagonist of Lucifer. Revelation 12:7.

Gabriel in Hebrew means God hath strengthened me, or the strength of God, or God is my strength. He is therefore fitly sent to announce the birth of John and to bestow upon him the spirit of power.