You shall have no other gods before Me. (Exodus 20:3)
We should fear, love, and trust in God above all things. (Martin Luther)
As simple as this commandment and Luther's explanation sounds, there's a lot here. What are we pursuing and treasuring? Material things? Pleasures? Philosophical or political ideals (other than God)? In what are we placing our trust and reliance? Our bank accounts and investments? Our retirement plan? Government and its laws and programs? Ourselves? Some spiritual leader? Some human concept of god? Stars or planets? Are we trying to do or control things that we should leave in God's hands (Hello? Husbands?!)?
None of these things are, of themselves, evil, and each can have a valid place in our lives. But they are all created things or the works of created beings. They (we!) are all subsidiary to the ultimate Creator, God. God belongs at the center of our life, not things He Created. We owe our existence and being - all of us - to God, in particular our love, trust, praise and worship, and reliance for things in life bigger than us.