We will conform to our image of God. Whatever our image of God is, we will make an effort—expend energy—to become like it. We had better be sure that it is the right image! Conforming will take place just as surely as a child born into a human family will conform to the image of that family—particularly the parents—and pick up their characteristics, whether they want to or not. This is a true principle, which Paul is speaking about here, only in a spiritual vein.
Since the Christian is to be "renewed in knowledge according to the image of Him who created him," he cannot be renewed in knowledge unless he is conforming to the right image. What Moses did when he was forty amounted to this: He knew about God, but he did not know God. He had head-knowledge of God, of the prophecy that God made to Abraham in Genesis 15:13-16, of the fact that the four hundred years were almost up, and that, counting Levi, he was of the fourth generation of Israelites who had been in Egypt.
He had head-knowledge, but he did not really know God. Therefore, he jumped the gun. Although he was excited and zealous, he was way off-base in terms of God's plan. However, in the intervening forty years, he came to know God. As he did, his beliefs about God changed, and thus his convictions also changed. They became more in harmony with the true knowledge of God.
Strong belief must be present, but it also must be right or it is out of sync with God. Those strongly held beliefs will not produce the right fruit because the way of life will not correspond with the true image of God. In other words, if our knowledge of God is not correct, it will not produce the right fruit because it does not conform to the true image of God.
At forty years of age, Moses' image of God was wrong. In his excitement and in his zeal, he went out, but he did not produce the right fruit. He could not because his image of God was incorrect. Forty years later, after spending so many years in the wilderness, his image of God was more correct, much clearer. Did it produce the right fruit? Yes, it did. Israel was released from its slavery because Moses was in harmony with God's will. The image of God was right, and he was conforming to it.
If our image of God is wrong, then our way of life will not be consistent with God's. Just like Moses, we need time for this process of coming to know God to take place.