From the very get-go, the Bible assumes that its reader already has a working belief in God, because it simply says, "In the beginning God created the heavens and the earth" (Genesis 1:1). The question is, how do we relate to God? And what does He really want from us?
The first of the Ten Commandments gives us a clue: God said, "I am the Lord your God, who brought you out of the land of Egypt, out of the house of bondage. You shall have no other gods before Me" (Exodus 20:2-3).
In other words, "This is who I am to you and this is what I've done for you, therefore, I want all of your devotion, worship, praise, and obedience. You are to worship and serve Me alone." This is the number one priority for us on God's top ten list.
There are three ways to look at this commandment: historically, pragmatically, and personally. Historically, we can understand why God would give this commandment to the children of Israel: they had come from Egypt and were going into Canaan, both places that practiced polytheism, the worship of many gods. And God wanted no rivals. In hearing that, some might think, Boy, God is pretty insecure. But it's actually just the opposite: because there truly are no other gods, God can be secure in saying, "I am God, and I want your utter devotion."
We can also understand pragmatically why God gave this commandment. Because He made us, He knows that nothing will satisfy our hearts except a relationship with Him. The Bible says we're subject to futility, or emptiness (see Romans 8:20), and we'll never be totally fulfilled until we're in a right relationship with the right God.
Finally, there's a personal side to why God gave Israel this commandment. He was in effect saying, "I'm your God by creation and by redemption--by delivering you from the land of Egypt. I now want to be your God by your devotion."
So ask yourself this: What do you think about in quiet moments? Like the needle of a compass when it's left to settle, where does your mind point? The Bible says, "As [a man] thinks in his heart, so is he" (Proverbs 23:7). If you discover that you don't think about God very much, then it's time to re-evaluate your life and your devotion to Him.
Again, God made us so that we won't be satisfied unless we're in a right relationship with Him, with no others beside Him. Is that who He is to you? Does He occupy first position in your life?