John Chrysostom — as excerpted in the Catena Aurea on Luke 1:18-22

“(sup.) 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?”