John Chrysostom
Considering his own age, and moreover the barrenness of his wife, Zacharias doubted; as it is said, And Zacharias said unto the angel, Whereby shall I know this? as if he said, “How shall this be?” And he adds the reason of his doubting; For I am an old man. An unseasonable time of life, an ill-suited nature; the planter infirm, the soil barren. But it is thought by some a thing unpardonable. in the priest, that he raises a course of objections; for whenever God declares any thing, it becomes us to receive it in faith, and moreover, disputes of this kind are the mark of a rebellious spirit. Hence it follows; And the angel answering said unto him, I am Gabriel, who stand before God.
That when you hear that I am sent from God, you should deem none of the things which are said unto thee to be of man, for I speak not of myself, but declare the message of Him who sends me. And this is the merit and excellence of a messenger to relate nothing of his own.
That the bonds might be transferred from the powers of generation to the vocal organs. From no regard to the priesthood was he spared, but for this reason was the more smitten, because in a matter of faith he ought to have set an example to others.
But the Angel says, And, behold; in other words, “At this instant.” But mark the mercy of God in what follows: Until the day in which these things shall be performed. As if he said, “When by the issues of events I shall have proved my words, and thou shalt perceive that thou art rightly punished, I will remove the punishment from thee.” And he points out the cause of the punishment, adding, Because thou believest not my words, which shall be fulfilled in their season; not considering His power Who sent me, and before Whom I stand. But if he who was incredulous about a mortal birth is punished, how shall he escape vengeance, who speaks falsely of the heavenly and unspeakable birth?