John 5:23-24
“And how,” says one, “can he that sends and he that is sent be of the same essence?” Again, you bring down the argument to carnal things, and perceivest not that all this has been said for no other purpose, but that we might know Him to be The Cause, and not fall into the error of Sabellius, and that in this manner the infirmity of the Jews might be healed, so that He might not be deemed an enemy of God; for they said, “This man is not of God”, “This man has not come from God.” Now to remove this suspicion, high sayings did not contribute so much as the lowly, and therefore continually and everywhere He said that He had been “sent”; not that you might suppose that expression to be any lessening of His greatness, but in order to stop their mouths. And for this cause also He constantly betakes Himself to the Father, interposing moreover mention of His own high Parentage. For had He said all in proportion to His dignity, the Jews would not have received His words, since because of a few such expressions, they persecuted and oftentimes stoned Him; and if looking wholly to them He had used none but low expressions, many in after times might have been harmed. Wherefore He mingles and blends His teaching, both by these lowly sayings stopping, as I said, the mouths of the Jews, and also by expressions suited to His dignity banishing from men of sense any mean notion of what He had said, and proving that such a notion did not in any wise apply to Him at all.
The expression “having been sent” denotes change of place— but God is everywhere present. Wherefore then says He that He was “sent”? He speaks in an earthly way, declaring His unanimity with the Father. At least He shapes His succeeding words with a desire to effect this.
Source: Homilies on the Gospel of John (New Advent)