This is another in a series of questions on the Bible.
Question: The Bible says that God flooded the earth to remove evil. If this is true, He failed, for evil is still here. In fact, evil never went away, for immediately after the flood, Noah got drunk.
In response, we must first realize that even if the account of the flood is as this question suggests, it does not argue against whether God exists or whether the Bible is true. Just because we might not understand why God does things, we still have good evidence that He exists and that the Bible is trustworthy.
Second, this falls into “why?” questions, and we will never know exactly why God does anything. We often do not know why we do things ourselves, so we, as finite minds, will not know the exact purposes of an infinite mind. God still has a rational, reasonable purpose for what He does, even if we do not understand it. A child does not understand why the parents do things, even though the parents have good, logical purposes for what they do.
Third, as is often the case, a simple comparing of the question to the passage in the Bible gives us the answer. The question is incorrect, for the Bible does not say that God flooded the earth to remove evil. Rather, Genesis 6:6-8 tell us that God flooded the earth to destroy people because He was grieved at the evil that humans had done. God, who is pure and holy, was repulsed by the evil in the world, and destroyed the people who had done evil. In God’s grace, He found favor with Noah and allowed him to live. The Bible never says that God wanted to destroy all evil in the flood with a goal of removing evil forever. Rather, it says that God judged the people of that day because of the specific evil that they did.
Fourth, the skeptic often puts God into an impossible paradox. If God allows some evil to continue, then questions like this one criticize God for not stopping evil. If God were to stop evil, such as when God commands the death of the Canaanites, the skeptic complains that God is unjust for doing so.
In the end, God is both just in punishing evil and loving for allowing fallible people like Noah to live. God, as the righteous judge, promises to make everything right in the end. He will someday punish all evil completely and reward all righteousness.
Lastly, this question recognizes that evil exists. It then grants the first premise of the moral argument for the existence of God. The fact that we can call anything in the world evil means that we have a standard of good and evil by which to measure the world. This standard cannot be in the world, but must be outside of the world, for if it were in the world we would not be able to measure the world by it. If God did not exist, then we are reduced to what atheists like Richard Dawkins claim, namely that there is no evil nor good in the universe. But since there is evil and good in the universe, we have an external standard by which to measure the universe. This we call God.