Luke 1:11-12

There appeared unto him an angel About four hundred years had passed since God had vouchsafed to his ancient people any supernatural communication, either by prophecy, the ministry of angels, or in any other extraordinary way. But as he was now about to send them the Messiah, and establish through him a new dispensation, by which a new and more spiritual way of intercourse with himself should be opened and settled, he sends an angelic messenger to announce his intentions, and prepare their minds for the reception of so great a blessing. For as the law, an inferior economy, was given at first, in a great measure, by the ministry of angels, it was proper that the gospel, a more excellent institution, should not want at least an equally extraordinary and honourable introduction. When Zacharias saw him, he was troubled Although he was accustomed to converse with God, yet we see he was thrown into a great consternation at the appearance of his angelic messenger, nature not being able to sustain the sight. Is it not then an instance of the goodness, as well as the wisdom of God, that the services which these heavenly spirits render us are generally invisible?