Gregory the Great — as excerpted in the Catena Aurea on Luke 1:18-22

“(Hom. xxxiv. in Evang.) For when angels come to us, they so outwardly fulfil 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.”