Basil of Caesarea

But let no one, hearing that the Lord had sworn to Abraham, be tempted to swear. For as when the wrath of God is spoken of, it does not signify passion but punishment; so neither dos God swear as man, but His word is in very truth expressed to us in place of an oath, confirming by an unchangeable sentence what He promised.

Catena Aurea by Aquinas ↗

Cyril of Alexandria

But let no one accustom himself to swear from hearing that God sware unto Abraham. For just as anger, when spoken of God, is not anger, nor implies passion, but signifies power exercised in punishment, or some similar motion; so neither is an oath an act of swearing. For God does not swear, but indicates the certainty of the event,----that that which He says will necessarily come to pass. …

Commentary on the Gospel of Luke ↗

Theophylact of Ohrid

Of what covenant did he speak, and of what oath given to Abraham? Without doubt, of this one: "In blessing I will bless you, and in multiplying I will multiply your seed" (Gen. 22:17). Abraham was indeed multiplied now, when all the nations through faith became his sons; for as he believed, so they too through faith became his sons.

Commentary on Luke ↗

Bonaventure

Secondly, he adds the establishing oath, when he says: The oath which he swore to Abraham our father: and the preceding word must always be repeated, namely performed: Genesis twenty-two: "By myself I have sworn, says the Lord, because you have done this thing and have not spared your only-begotten son for my sake, blessing I will bless you." Introducing this, the Apostle in Hebrews six says: "For God, promising to Abraham, since he had no one greater by whom he might swear, swore by himself"; and thus, so that "he might show more …

Commentary on Luke, Chapter 1 ↗