Here are three questions I asked a Christian friend of mine followed by his response:
1. How do we understand evil through practical experience?
2. What makes something good?
3. If men can do evil, then can they create beauty / do good things?
3. I cannot think of one thing that man has done where he/she has created something beautiful. That may sound shocking, but what I mean is that anything man creates, whereby I assume you mean some kind of art or fabrication, is only beautiful to another person to the degree you can appreciate another's creativity and expression of that creativity. I've never known or read about someone who could not appreciate the beauty of God's creation, which man has slowly been destroying or manipulating to his advantage. So, that which God has made is beautiful…things that man makes are subject to scrutiny.
2. When men do good things, it's only if they follow God's ways. His ways are always righteous, just, good and true. When someone practices mercy, they participate in the divine way, even if they are pagan. Doing good things doesn't make one a good person. Doing what is good, ultimately, comes from being in tune with God. Jesus always did what was good because he was in tune with His Father; but those around him subjected his words and deeds to careful scrutiny and didn't always agree with who he was and what he did. But Jesus knew that anyone who wanted to do God's will would know that His teaching was from God (John 7). His teaching always promoted what was good, beautiful, righteous, merciful and true. That's why he could tell Pontius Pilot that everyone on the side of truth listened to him.
1. People understand evil as they remain true to their conscience. No matter what tribe you visit, there will be something set up in the social order that corresponds to what is universally felt as evil: Homicide, rape, thievery, adultery, pillage, etc. People have a sense of when injustice and iniquity is committed against them. There is an element of Common Sense to that because we've all been hard-wired to understand something of our universal rights as human beings who respect the rights of others. It's obviously different degrees for different groups of people, so there isn't a hard and fast rule to be applied because different civilizations are complex. But something of the ways of God is always somewhere etched into their existence.
Finally, the existence and power of God is really a mute issue. Unfortunately, not many people know of the mighty deeds God does for His people and the miracles He performs in other countries in the name of His Son, Jesus the Christ, in order to validate His ministry and His triumph over sin, death and hell. Demons surrender to him, Dead men walk, lepers are still cleansed, blind men still receive sight, and deaf men still hear (and I'm not talking on a spiritual basis, though that is also true). God is physically healing and supernaturally restoring people to new life in Jesus Christ. He is letting them experience His power so that they have a testimony to share of the victory in Jesus. Our modern Western culture sees so little of this power because it needs so little of it. We are too comfortable, too intellectual, and too ingenuitive to seek God's intervention. But God is and His power is alive for those who put their trust in Jesus.
Hope this helps.