11 And now I will put before you examples from the Law. Eliseus was sought by the king of Syria; an army had been sent to capture him; and he was surrounded on all sides. His servant began to fear, for he was a servant, that is, he had not a free mind, nor had he free powers of action. The holy prophet sought to open his eyes, and said: “Look and see how many more are on our side than there are against us.” And he beheld, and saw thousands of angels. Mark therefore that it is those that are not seen rather than those that are seen that guard the servants of Christ. But if they guard you, they do it in answer to your prayers: for you have read that those very men, who sought Eliseus, entered Samaria, and came to him whom they desired to take. Not only were they unable to harm him, but they were themselves preserved at the intercession of the man against whom they had come.
Source: Sermon against Auxentius (New Advent)