You shall have no other gods.
What does this mean? We should fear, love, and trust in God above all things.
Being Lutheran, I believe that Scripture contains both Law and Gospel.
The Law in the First Commandment is, of course, the prohibition against idolatry, having other gods. Idolatry happens whenever we replace God with something else or when we worship a god that is not the Triune God. Anything or anyone can replace God: money, sex, drugs, alcohol, power, movie stars, pro athletes, etc. Even something as seemingly harmless as body image can be distorted in such a way as to be idolatrous.
The Gospel in the First Commandment is that God gives us Himself as our God. God is not just any god. God is the Triune God, the Father, the Son and the Holy Spirit. God is the creator of all things. God is the God of Abraham, Isaac, and Jacob. God is the God who sent his only Son to die on a cross for the sins of the world. Because God has done all of this, we are to worship Him and Him alone