Church Fathers on Luke 1:21

Considering his own age, and moreover the barrenness of his wife, Zacharias doubted; as it is said, And Zacharias said to 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…

As if he says, “If it were man who promised these miracles, one might with impunity demand a sign, but when an angel promises, it is then not right to doubt. It follows; And I am sent to speak to you.

For when angels come to us, they so outwardly fulfill their ministry, as at the same time inwardly to be never absent from His sight; since, though the angelic spirit is circumscribed, the highest Spirit, which is God, is not circumscribed. The angels therefore even when sent are before Him, because on whatever mission they go, they pass within Him.