God could have created us as mindless automatons yet He made us with free will to chose and decide on things for ourselves. When we sin, we chose to break God's law. Hence to say that evil didn't exist until God willed it into existence would not make sense, since evil is chosing not to follow God's law. That's a choice the individual makes. The first individual to make that choice was Lucifer.
This whole controversy about sin and Satan's whole crusade is about discrediting God. He want's to paint the picture that God is a hypocrite, unfair, and cruel. Satan want's all to believe that God sets these laws that are impossible to keep, and that He sets us up to fail. Satan wants all to believe that God is a bully who exerts His will on others and forces them to obey. The devil is putting God on trial. God intends to show all that the devils claims are all false. God want's us to worship Him out of love, not by force. Hence He gave us free will to chose Him.
This is why Jesus came to earth as a human being just like us to go through life like us and face all the same temptations like us. Through that experience Jesus proved to mankind that it was possible life of obedience to God's law. Jesus purpose on earth was also to expose us to the true nature of God.
Jesus showed us God's nature through His sacrifice, and His acts of love and spreading of the Gospel.
God is love. God has always been about love. God's laws were created out of love as a prescription for how to live a life that ensures happiness through freedom from sin. The basic principle of God's law is love.
Matthew 22
1 John 4 KJV37 Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind.
38 This is the first and great commandment.
39 And the second is like unto it, Thou shalt love thy neighbour as thyself.
40 On these two commandments hang all the law and the prophets.
God's nature of Love is shown clearly in His plan of salvation for the human race. He loves us so much that He does not want any of us to perish. That is why He must eliminate sin and it's attachments, and that is why He sent Jesus to die for us.7 Beloved, let us love one another: for love is of God; and every one that loveth is born of God, and knoweth God.
8 He that loveth not knoweth not God; for God is love.
John 3:16
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.