Because God is absolutely good and the Source of all good, anything that is different than His will is evil by the very fact that it is different. This is what evil is and how it exists: it is whatever is different than the will of God.
In the universe God created and through all eternity prior to creation, evil did not exist. There was no such thing until Lucifer desired more than the glory with which God had already created and endowed him.
In the garden of Eden, the serpent tempted the woman, telling her it was important to decide what is good. “Is it good for God to impose limitations? Is it right that He withholds knowledge from you? Is there something better for you? What would be best?”
“When the woman saw that the tree was good for food, and that it was a delight to the eyes, and that the tree was desirable to make one wise, she took from its fruit and ate” (Gen 3:6).
The moment the man decided that good was not good, the purity and innocence of nakedness, with which the couple was blessed and in which they were guarded, became a problem they could not accept, resolve, or cover. Mankind was locked into a need to form judgments about good at the same instant he compromised and ruined human nature so that it could never be good again.
“Transgression speaks to the ungodly in the innermost part of his heart;
There is no fear of God before his eyes.
For it flatters him in his own eyes
Concerning the discovery of his iniquity and the hatred of it” (Ps 36:1-2).
In their need to accept themselves, individuals attempt to live in a way that is worthy of approval and conform their behavior to standards of law. But, convicted and aware of their compromises and failures, they resort to their own evaluations and adopt their own manageable standards of good.
“For when Gentiles do instinctively the things of the Law, these, not having the Law, are a law to themselves, in that they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them” (Rom 1:14-15).
“The fear of the Lord is the beginning of wisdom” (Prov 9:10). The only acceptable and safe response for mankind is to embrace His will and standard for human life and to be conformed to it. But we are helpless to rise above our preferences.
When Jesus, the Son of God, came into the world to reconcile men to the Father, His first objective was to live so that His entire life was worthy of the Father’s approval. This is what He desired and set His heart and will to do:
“When He comes into the world, He says, . . . “Behold, I have come to do Your will, O God” (Heb 10:5, 7).
“I can do nothing on My own initiative. As I hear, I judge; and My judgment is just, because I do not seek My own will, but the will of Him Who sent Me” (John 8:30).
Jesus gave this “good” life of His in exchange for ours at the cross, and now He lives by His Spirit in each of us who receive Him, making our lives good and worthy of God’s approval. He is the Second Adam, creating in Himself a new race that delights in doing our Father’s good and perfect will. He delivers us from ourselves. He delivers us from evil.
(Spotlight 5, Lesson 9 in Doctrine 101: Learning about God)