In Isaiah 55:1 and 2 God invites us to go shopping. We have no currency or credit of our own with which to buy. Jesus Christ is the currency, a voucher with our name on it, an open unlimited line of credit. Our problem without Jesus Christ is more than just a lack of currency. We have been shopping in the wrong market and buying the wrong products. God's market is full of that which is good or as the verse 2 puts it, "let your soul delight itself in fatness."