Why didn’t God destroy Satan earlier?

Answer:

"Blessed is a man who perseveres under trial; for once he has been approved, he will receive the crown of life which the Lord has promised to those who love Him. Let no one say when he is tempted, "I am being tempted by God"; for God cannot be tempted by evil, and He Himself does not tempt anyone. But each one is tempted when he is carried away and enticed by his own lust" (James 1:12-14).

People grow when they overcome difficulties. Thus, coaches push athletes to run, lift weights, and do other miserable things so that they become stronger when the real test comes in the competitions. God pushes us to grow by having us face trials and temptations. Yet, God cannot directly tempt people to sin because it is against His nature, so He allows Satan and his minions to make life difficult for people within the limits God sets. "No temptation has overtaken you except such as is common to man; but God is faithful, who will not allow you to be tempted beyond what you are able, but with the temptation will also make the way of escape, that you may be able to bear it" (I Corinthians 10:13).

We can see this illustrated when Israel was in slavery in Egypt. God allowed a wicked Pharaoh to arise who made the Israelites lives difficult. That caused the Israelites to appeal to God for deliverance, which He did provide, but it also caused all the Israelites to want to leave Egypt when Moses led them out. God also used Pharaoh's stubbornness to demonstrate His power and God's reputation then protected the Israelites as they migrated to the land of Canaan.

Satan's final end has been declared and it is certain. But in the meantime, God makes use of Satan to cause people to want to leave sin and follow God. Satan's antics also gives people a choice, so his temptations clarify who really desires God and who don't care.