What is the source of evil?

Romans 3:23Everyone has sinned; we all fall short of God’s glorious standard.

Romans 7:18-23I know that nothing good lives in me, that is, in my sinful nature. I want to do what is right, but I can’t. I want to do what is good, but I don’t. I don’t want to do what is wrong, but I do it anyway. But if I do what I don’t want to do, I am not really the one doing wrong; it is sin living in me that does it. I have discovered this principle of life—that when I want to do what is right, I inevitably do what is wrong. I love God’s law with all my heart. But there is another power within me that is at war with my mind. This power makes me a slave to the sin that is still within me.

Since Adam and Eve sinned (see Genesis 3:1-19), humanity has been infected and born with a sinful nature. We are born with a spiritual disease that causes us to sin—the desire to go our own way instead of God’s way. The proof of this is that no one has ever lived a perfect life (except Jesus, God’s Son). So while we can work to sin less, and to keep sin from controlling us, we can never—on this side of the Kingdom of God—eliminate sin altogether.

Jeremiah 17:9-10“The human heart is the most deceitful of all things, and desperately wicked. Who really knows how bad it is? But I, the Lord, search all hearts and examine secret motives. I give all people their due rewards, according to what their actions deserve.”

Our own hearts, polluted by sin and selfishness, can tempt us into evil thoughts and actions.

Ephesians 6:12We are not fighting against flesh-and-blood enemies, but against evil rulers and authorities of the unseen world, against mighty powers in this dark world, and against evil spirits in the heavenly places.

Cosmic forces of evil, led by Satan, are engaged in a deadly rebellion against God and against us personally if we claim allegiance to God.