Thou shalt have no other gods before Me
In his explanation of the First Commandment, Martin Luther gives a clear definition of who God is and who God is not. “That to which your heart clings and entrusts itself is, I say, really your God.” This statement makes it clear that all people have a “god.” The question for Christians is “who is your god – money, power, prestige or the one true God, creator of heaven and earth?” If the answer is God, Lord of All, it is in him whom we place all our trust and confidence. The results of this complete trust in God is willing obedience to this and the rest of God’s commandments – not through coercion or a sense of duty, but out of love and gratitude.
Luther’s Small Catechism
Q. What does this mean?
A. We are to fear, love, and trust God more than anything else.
From Luther’s Large Catechism
1] That is: Thou shalt have [and worship] Me alone as thy God. What is the force of this, and how is it to be understood? What does it mean to have a god? or, what is God? 2] Answer: A god means that from which we are to expect all good and to which we are to take refuge in all distress, so that to have a God is nothing else than to trust and believe Him from the [whole] heart; as I have often said that the confidence and faith of the heart alone make both God and an idol. 3] If your faith and trust be right, then is your god also true; and, on the other hand, if your trust be false and wrong, then you have not the true God; for these two belong together, faith and God. That now, I say, upon which you set your heart and put your trust is properly your god.
4] Therefore it is the intent of this commandment to require true faith and trust of the heart which settles upon the only true God, and clings to Him alone. That is as much as to say: "See to it that you let Me alone be your God, and never seek another," i.e.: Whatever you lack of good things, expect it of Me, and look to Me for it, and whenever you suffer misfortune and distress, creep and cling to Me. I, yes, I, will give you enough and help you out of every need; only let not your heart cleave to or rest in any other.
28] Let every one, then, see to it that he esteem this commandment great and high above all things, and do not regard it as a joke. Ask and examine your heart diligently, and you will find whether it cleaves to God alone or not. If you have a heart that can expect of Him nothing but what is good, especially in want and distress, and that, moreover, renounces and forsakes everything that is not God, then you have the only true God. If, on the contrary, it cleaves to anything else, of which it expects more good and help than of God, and does not take refuge in Him, but in adversity flees from Him, then you have an idol, another god.
Large Catechism Text in the public domain. http://bookofconcord.org/lc-3-tencommandments.php