This post was originally published in February 2017. –ed.
When we think of idolatry we usually think of a primitive pagan in a mud hut bowing down to a little god on the ground, or we imagine a pagan temple, very elaborate and ornate with a lot of burning incense. But idolatry goes beyond the idea of creating a false God. Fundamentally, idolatry is thinking thoughts about God that are untrue of Him, or entertaining thoughts about Him that are unworthy of Him.
In that sense, many evangelicals are guilty of idolatry. I am appalled at what some Christians assume God to be. God is appalled, too, when He says in Psalm 50:21, “You thought that I was just like you; I will reprove you, and state the case in order before your eyes.” Contemporary Christianity has lowered God to its level, robbing Him of majesty and holiness. That is as idolatrous as worshiping a rock.
Yet that is precisely what many have done. They have made a false god in their own likeness. Their thoughts about Him come from the imaginations of their own minds, and have nothing to do with what He really is like.
A. W. Tozer wrote,
The history of mankind will probably show that no people has ever risen above its religion, and man’s spiritual history will positively demonstrate that no religion has ever been greater than its idea of God. Worship is pure or base, as the worshiper entertains high or low thoughts of God.
For this reason the gravest question before the Church is always God Himself, and the most portentous fact about any man is not what he at a given time may say or do but what he in his deep heart conceives God to be like. 
The most basic truth in worship, then, is the worshiper’s understanding of God.
In Hosea 6:6 the Lord says, “I delight in loyalty rather than sacrifice, and in the knowledge of God rather than burnt offerings.” That statement elevates the knowledge of God to a position of supreme importance.
Proverbs 9:10 says, “The fear of the Lord is the beginning of wisdom, and the knowledge of the Holy One is understanding.” No one is wise until he knows God; no one has even the slightest understanding until he has the knowledge of the Holy One. Without the knowledge of God, all worship is unacceptable worship, not any different from the grossest idolatry.
We get into trouble when we try to make God too much like what we know. When we use human symbols to describe God, we must remember that He is the ultimate, infinite pattern and not the copy. No metaphor can fully explain God. For example, we understand God’s love because we know human love. But when God’s love behaves unlike our love we must not assume that God’s love is faulty. That is making human love the absolute pattern and judging God’s love by it.
It is often easier to think of God in negative terms. We live in a world that is so opposite God that we frequently have to grasp what God is like by saying what He is not like, because He is unlike anything we understand. For example, when we say God is holy, we mean He has no sin. We cannot conceive of the essence of absolute holiness—all we have experienced is sin. We cannot comprehend eternality or infinity, but we understand boundaries, so we say that God doesn’t have any limitations.
But can we understand God? The Bible says we can. We can never fully comprehend Him but we can certainly understand true things about Him. That is because God has revealed Himself to us not only in His creation, but more specifically in His Word. It is our duty to understand His self-revelation accurately.
Yet the temptation is always strong to conform God’s character to our pattern of thinking. And that’s fraught with danger when we live and function in a world that is constantly changing.
The very concept of an unchanging God is incompatible with a world shaped and driven by scientific discovery, constantly evolving technology, and self-determined morality. The cultural expectation to “change with the times” is invariably applied to God as well. His justice is expected to shift and slide with the standards of our times—a presumed leniency that accommodates our sinful preferences and propensities.
But those are dangerous assumptions that offer false comfort. They fly in the face of Scripture’s clear testimony about God’s unchanging character and nature—in theological terms, His immutability.
In the days ahead we’ll explore the biblical record concerning God’s immutability. Moreover, we’ll consider the great assurance we can draw from knowing the fixed nature of God’s irreversible promises—the ultimate comfort that comes from worshiping the One true unchanging God.
Used with permission from John MacArthur.