God promises to provide great feast for the Hebrew people. This is something special, as one might expect of a meal from God. Rather than laboring for a bare subsistence, God promises to provide a rich food more than the simple manna given at the first exodus to Moses and the people as they left Egypt. God tells the people not to waste their time and money on the ordinary in life, but to enjoy that which only God can provide them. God calls on the people to listen to him, just as David listened, and to be witnesses to him, just as David was a witness.
Life is about to change.
Then, in the midst of the oracle of the Lord, the prophet speaks. Isaiah calls on the people to come back to the Lord their God. Come back, Isaiah tells the people, and be repentant. Instead of the status quo, the prophet calls the people to give up their wickedness and come to the Lord so that the Lord can show mercy on them and pardon them. The words of the Lord and the prophet don t require the people to give up everything, but to give up those things that are not important to their salvation.