As God works to provide an opportunity for human beings to be holy as He is holy, divine judgment is also the work of God. Judgment occurs because it is the consequence to one's sin evaluated against God's holy nature and moral standard.

This is readily seen in the Old Testament where God actively rules and judges nations. A good example is when Moses speaks to the nation of Israel just before the Conquest.

Do not say in your heart when the Lord your God has driven them out before you, "Because of my righteousness the Lord has brought me in to possess this land," but it is because of the wickedness of these nations that the Lord is dispossessing them before you. It is not for your righteousness or for the uprightness of your heart that you are going to possess their land, but it is because of the wickedness of these nations that the Lord your God is driving them out before you, in order to confirm the oath which the Lord swore to your fathers, to Abraham, Isaac and Jacob. (Deut 9:4-5)

In the New Testament, God's work of judgment is less apparent, because Jesus Christ is portrayed as the divine judge who will judge the world in the future at the end of history. However, God's work sets an example for His Son to follow (John 5:19-20), and it is God who gives Jesus this privilege of judgment.

For not even the Father judges anyone, but He has given all judgment to the Son, so that all will honor the Son even as they honor the Father. He who does not honor the Son does not honor the Father who sent Him. (John 5:22-23)

In fulfillment of His promises and covenant to Abraham, God's work of judgment is part of His sovereign plan for the world. This is readily apparent in the book of Revelation, where God is the author of the scroll containing the judgments that take place:

I saw in the right hand of Him who sat on the throne a book written inside and on the back, sealed up with seven seals. And I saw a strong angel proclaiming with a loud voice, "Who is worthy to open the book and to break its seals?" (Rev 5:1-2)

To learn more, see:

What Does "Judgment" Mean?

God's Work of Judgment