Theophylact of Ohrid

For the manner in which the forerunner prepared the way of the Lord he explains, adding, To give knowledge of salvation. The Lord Jesus is salvation, but the knowledge of salvation, i. e. of Christ, was given in John, who bore witness of Christ. For in no other way was He known to be God, but as having forgiven the sins of His people. For it is of God alone to forgive sins.

Catena Aurea by Aquinas ↗

Bede

To give the knowledge of salvation to His people by the remission of their sins. As if desiring to expound and commend the name of Jesus, that is, Savior, he frequently mentions salvation, recalling to be raised the horn of salvation, salvation to come from enemies, knowledge of salvation to be given to His people. But lest you think a temporal and carnal salvation is promised, he says, in the remission of their sins. …

On the Gospel of Luke ↗

Bonaventure

He commends it also secondly from the utility of the doctrine, when he says: To give knowledge of salvation to his people: to give, namely freely: Matthew 10: "Freely you have received, freely give"; and Proverbs 2: "The Lord gives wisdom, and from his mouth come prudence and knowledge." To give, I say, knowledge, not just any, but of salvation: because without knowledge there is no salvation; Isaiah 5: "Therefore my people has been led captive, because it did not have knowledge." This every ruler of the people ought to have; Hosea …

Commentary on Luke, Chapter 1 ↗