He is discussing the first commandment: "You shall have no other gods."
What is it to have a god? What is God?
Answer: A god is that to which we look for all good and in which we find refuge in every time of need. To have a god is nothing else than to trust and believe him with our whole heart. . . .
The purpose of this commandment, therefore, is to require true faith and confidence of the heart and these fly straight to the one true God and cling to him alone. "The meaning is; 'See to it that you let me alone be your God, and never seek another.' In other words: 'Whatever good thing you lack, look to me for it and seek it from me, and whenever you suffer misfortune and distress, come and cling to me. I am the one who will satisfy you and help you out of every need. Only let your heart cling to no one else.
. . . . Many a person thinks he has God and everything he needs when he has money and property; in them he trusts and of them he boasts so stubbornly and securley that he cares for no one. Surely such a man also has a go--mammon by name, that is, money and possessions--on which he fixes his whole heart. It is the most common idol on earth. He who has money and property feels secure, happy fearless, as if he were sitting in the midst of paradise. On the other hand, he who has nothing doubts and despairs as if he never heard of God. Very few there are who are cheerful, who do not fret and complain, if they do not have mammon. . . .
So, too, if anyone boasts of great learning, wisdom, power, prestige, family, and honor, and trusts in them, he also has a god, but not the one, true God. Notice, again, how presumptuous, secure, and proud people become because of such possessions, and how despondent when they lack them or are deprived of them. Therefore, I repeat, to have a God properly means to have something in which the heart trusts completely."
- In The Book of Concord: The Confessions of the Evangelical Lutheran Church, translated and edited by Theodore G. Tappert (Philadelphia: Muhlenberg Press, 1959), 365-66.