"'The words 'I am thy God' are the standard and measure of everything that can be said about worship.'" These words of Luther show that God and worship belong together. A person's picture of God determines his idea of worship. Indeed, the First Commandment is basic for Luther's idea of worship. Faith itself is the essence of worship; for faith is the fulfillment of the First Commandment, and idolatry is nothing but unbelief. Man must decide between worship and idolatry. There is no other choice. Either God is "our God," and we live in fellowship with him, or else by distrust despise him. The one implies worship, the other idolatry."
Vilmos Vajita, Luther on Worship: An Interpretation (Philadelphia: Muhlenberg, 1958), 3.