He ordained it as a testimony for Joseph when he went out over the land of Egypt, where I heard an unfamiliar language:
PSALM 81 This psalm consists of two parts. Whoever was its author, he exhorts the people to remember the unparalleled grace of God towards them, in delivering them by his outstretched arm, and choosing them to be a kingdom of priests, and a peculiar Church to himself; that thus they may be excited devoutly to honor their deliverer, both by celebrating his praises, and by leading a holy life.
Commenting on Psalm 81:1-16
This he ordained in Joseph for a testimony. The nation is called Joseph, because in Egypt it would probably be known and spoken of as Joseph's family, and indeed Joseph was the foster father of the people. The passover, which is probably here alluded to, was to be a standing memorial of the redemption from Egypt; and everything about it was intended to testify to...
When the people of God were gathered together in the solemn day, the day of the feast of the Lord, they must be told that they had business to do, for we do not go to church to sleep nor to be idle; no, there is that which the duty of every day requires, work of the day, which is to be done in its day. And here, I.
Commenting on Psalm 81:1-7