You shall have no other gods before me (Exodus 20:3).
To have a god, according to the sixteenth-century reformer Martin Luther, is “to trust and believe in that one with your whole heart. . . . You lay hold of God when your heart grasps him and clings to him.” And so, this first command tells us that, because God is our redeemer and because we are in relationship with him, we should grasp and cling to no one else besides the Lord. No other love should take priority over him; no other love should be placed alongside or substituted for him. No other love should be set in confrontation with the Lord in a test or trial. Because we are in relationship with God through his redeeming work, we are called to an exclusive devotion to and a thorough delight in him.
Adapted from the Gospel Transformation Bible