What is evil? Evil is not really the existence of something as much as it is the absence of something. Evil is the absence of good. It is a result of man living for himself instead of in the righteous way he was designed to live. It is, thus, a product of the God given free-will of man. God could have created men as robots with no freedom. They could then be “good” and love Him because He makes them do that, but would that be love? Would love keep us from harm so much so that it suffocates us into mindless obedience to a Will more powerful than our own to which we have no choice, but to serve? I think we can emphatically answer no. Therefore, the way of love is for God to create humans who can chose to love Him and live ensconced in His love or they can reject Him and live as they please.

Now living contrary to our created purpose will be harmful and against what is good, pure, and holy. It will have consequences because the way of sin leads to death. That is the natural order of things. If something leaves its natural habitat where it belongs and enters an unnatural habitat there will be a significant depletion of its vitality. It is the same for humans. If we live contrary to our created habitat of existence, which is in communion with our life source, God, then we begin to lose the fullness of life and we live in a counterfeit reality. We need our roots to be in God to have the fullness of life. When our roots are in this world instead we do not obtain enough sustenance to be complete. When our nature took on sin when Adam chose to go his own way, humanity was altered, depleted in a sense from our intended nature. Adam spiritually and physically caused a change of events in all humanity. But God is a loving and good God and despite our digging our roots into nature instead of His Super-nature, He in His grace and mercy provided a way to protect us from the consequences of sin. He did this by the most loving act of sacrifice of His own Son who is of His substance, God. This redemption provided by the death and resurrection of Jesus Christ was not just for those who trust in Jesus after this event, but for all those who looked forward to the promise of redemption before this event. All of creation climaxed and culminates in the redemptive act of Christ. All that was depleted can find restoration in Christ because of His sacrifice.
Why did God have to do it this way? Why not just forgive all our sins with no sacrifice? Or why not just let us do as we please and give us all eternal bliss anyway? The wages of sin is death. Death, physically and spiritually, is the result of sin in the natural order of things. So either we continue in that death—that separation from the life source of God or He dies in our place and substitutes Himself to pay the price that we would have had to pay to protect us and restore us by His works and not by ours. So while all men sin and none are good by themselves. He paid our debt of sin. He suffered so we wouldn’t have to. What greater love can there be? What greater goodness?
You see, eternal life is more than heaven. Heaven is a place where our life continues after the natural body dies, but it is an extension of our source of life while we are living on the earth. If we are in God on earth, we continue the same way upon natural death. We continue that life with God. If we reject God on earth we continue in that place of rejection after death. It’s the state we exist in by our choice, not by His punishment. Eternal life happens when we accept the free gift of the forgiveness of God through Jesus. He promises that He will dwell within us, and commune with us, changing our nature to a redeemed nature versus our nature that is tied to death and the earth due to sin.
I was asked in a comment that if a Christian’s nature is changed why are some atheists more moral than some Christians? It would appear there is nothing to this whole idea that somehow Christians are changed for they are not better in their actions than anyone else who strives to be moral.
The answer is that while spiritually we are made new, sometimes it takes some time for that to mature in outward changes. It is a process of growth in Christ. Some Christians are in a place where they accepted His forgiveness and they have His eternal life, but they never left infancy in their relationship with Him. Sometimes it’s because they held on to some parts of their lives that they did not want to surrender to God and God’s still working out a process of redemption in those areas. Each person’s relationship with God is different and its own journey. There are not to be cookie cutter Christians who are all in the same robotic state of maturity in Christ because they said some prayer and now everything in their life is all-good. Upon accepting God’s forgiveness and coming into relationship with Him, you are at that moment under His grace and mercy and His justice justifies you as holy and pure in His sight. But in the natural there are things that still persist from the old life that often times can take time to work out. You do not suddenly loose your will and become a perfect moral puppet serving God’s every whim. You still have control of your mind, will, and emotions and you still are in a learning process of what it means to know and trust God. God is patient with us and He is kind. Our struggles or our doubts do not offend Him. So you’ll find Christians at all different places in their walk with God.
The important thing is looking at ourselves and our own distance from God. We can’t get to God by being good or being religious or any other way we can come up with by our own ideas. The only way to God, is God coming to us. He has done that through Jesus opening the door for anyone who wants to step through and walk a new walk by His loving strength; therefore entering a new supernatural reality that is more real than our counterfeit realities we derive by our unaided reason. He is the reason we can reason and yet we use it to deny Him instead of to come to Him for even our reason has been adversely affected by the sinful nature. When we use it without Him being our source of truth, we use it in a limited fashion and not in its fullness.