From mountain to mountain, from meal to meal the LORD God points us to His banquet, already prepared; the marriage feast of the Lamb in His Kingdom which shall have no end!
Isaiah first reminds the people of who they are and then tells them why they are who they are; to bring the teachings and promises of the LORD to all people.
This food, already purchased and freely given in our pericope, is a foretaste of the feast to come as well; the marriage feast of the Lamb in His Kingdom which has no end.
To dwell with a Holy God in their camp, Israel lead holy lives. Anything standing in the way of and threatening this holy relationship must be avoided or eliminated.