I am the Lord your God, who brought you out of the land of Egypt, out of the house of slavery.
You shall have no other gods before me. (Exodus 20:2-3 ESV)
To keep the commandment to worship the Lord our God and no other god, we need to know him as he has revealed himself. When our view of God is skewed, it isn’t quite the one true God we are holding in our minds when we worship. To the extent that our view of God is different than his self-revelation, we are “exchanging the truth of God for a lie” (Romans 1:25)—and that's idolatry. This is why the Westminster Larger Catechism lists ignorance and misapprehensions of God right beside unbelief and misbelief in the list of sins forbidden by the first commandment.
We can't excuse our ignorance of God by thinking there's no use trying to understand what he is like him because he is incomprehensible. It is true that God is incomprehensible. He’s infinite and we have pea brains. R. C. Sproul says we are like infants struggling to understand a genius.1 We will never, ever, not in a million years or eternity, understand the whole of who and what God is.
But God identifies himself to his people immediately before he gives this command. “I am the Lord your God who brought you out of the land of Egypt . . . .” The incomprehensible God tells them something about himself, something he has done for them, something they can understand, so they can focus on him when they worship. They could know him, not fully, but truly, because of his self-revelation.
We have even less excuse for ignorance than the Israelites did, because in all of scripture, God is defining himself for us. In the Bible, says Sproul, the genius is speaking to the infant in the infant’s own terms.2 God condescends to speak to us in language we can understand. We can know him, never fully, but truly, because he tells us about himself and his works.
It’s always worth the effort it takes to understand God’s revelation of himself, because the more we learn of his character and actions, the more we are able to see him as he really is. The more we know, the more it is the one true God we hold in our minds when we worship.
Have you ever heard someone say that obedience matters more than theology? I have—and it's a silly statement. Commandment number one makes knowledge of God, or theology, fundamental to obedience. Obedience starts with theology—knowing what can be known about God, what he has shown to us (Romans 1:19)—so there is less idolatry and more truth in our service.
1R. C. Sproul, Truths We Confess
2Same as above