Among the trees of Eden was the Tree of the Knowledge of Good and Evil. Notice it was not the tree of good and evil, but the knowledge of good and evil.
God Himself has the knowledge of good and evil, as Satan said: “For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil." (Genesis 3:5)
It is my belief that when Christ created the angelic creatures in the beginning they were not given an understanding of the way of righteousness, that is, of the knowledge of good and evil. Perhaps that is why Satan emphasized that God knows good and evil, the implication being that only God knows good and evil.
It may be a fact that angels and people had no authoritative code of righteous behavior prior to the writing of the Ten Commandments.
It is our conscience that distinguishes good from evil, although our conscience before Christ matures in us is largely unformed. It may be true that angels do not have a conscience. They may have a sense of duty and loyalty to God (at least some of them do), but they do not have the ability to judge moral issues.
Perhaps this is why there are two armies that do the will of God. There is the army of warrior angels; and then there is the army of saints who make moral judgments and give their decisions to the warrior angels to carry out the sentences that have been handed down.
