John Gill Commentary Psalms 77:15

"Thou hast with thine arm redeemed thy people, The sons of Jacob and Joseph. Selah" — Psalms 77:15 (ASV)

You have with your arm redeemed your people
The people of Israel out of Egypt, which was typical of the redemption of the Lord's people by Christ, the arm and power of God:

the sons of Jacob and Joseph .
Joseph is particularly mentioned for honour's sake, and because he was the means of supporting Jacob and his family in Egypt; and had special faith in their deliverance from there; the Targum is, ``the sons whom Jacob begot, and Joseph nourished.'' Selah. (See Gill on Psalms 3:2).