Ambrose of Milan
Catena Aurea · Lukasevangelium 1
And there appeared unto him an angel of the the Lord standing on the right side of the altar of incense. And when Zacharias saw him, he was troubled, and fear fell upon him. But the angel said unto him, Fear not, Zacharias: for thy prayer is heard; and thy wife Elisabeth shall bear thee a son, and thou shalt call his name John. And thou shalt have joy and gladness; and many shall rejoice at his birth.
It was not without good reason that the angel appeared in the temple, for the coming of the true High Priest was now announced, and the Heavenly Sacrifice was preparing at which angels were to minister. For one cannot doubt that an angel stands by where Christ is sacrificed. But he appeared at the right hand of the altar of incense, because he brought down the token of Divine mercy. For the Lord is on my right hand, so that I should not be moved. (Ps. 16:8.)