(רַע ra [Calamity]; πονηρός poneros [Malignant]; κακός kakos [Wrong])
In Genesis we are first introduced to the concept of evil when God instructs Adam that he is not to eat from the tree of the knowledge of good and evil (Genesis 2:17). From God’s command we see that evil is in contrast to good. However, what is good and what is evil? We see good described within the renovation of the earth when God brought the land out of the water, for the earth was in chaos because of the judgment that came upon Lucifer (Ezekiel 28:13, 16; Genesis 1:2), made the atmosphere, sun and moon, and biological life before He created humans to rule over the earth. All of these things He did and made are called good, which describes them as beneficial; therefore, evil is that which causes calamity, for it is not beneficial.
Within about seventeen hundred years from Adam disobeying God and bringing death upon the whole human race, evil was so bad in the hearts of humans that it was the only formation of the thoughts all day long (Genesis 6:5). In a description of Sodom, the men are described as being men of evils and sins, which informs us that not all evil is considered sin. Evil also describes the determination within the mind to do something that is wrong, not just that act itself. Therefore, rather than doing what is right and beneficial, evil is describing doing something that lacks in character, along with the mindset that brings about such immoral actions, which is unrighteousness (All sin has a quality of unrighteousness – 1 John 5:17).
Our conscience also helps define evil, for it either accuses or excuses our actions (Romans 2:15). It does this by comparing what we know we should do and how we should act against what we are actually doing. However, it is not the final rule on what is good, for it can be incorrectly trained by lies which impact our beliefs and actions (1 Corinthians 8:7); therefore, our conscience needs to be based upon truth, for truth is seeing things as they really are and if our hearts condemn us, God is greater than what we know within our conscience so it should always be corrected by what He says (1 John 3:20).
Evil comes in two forms, a person that does things that lack in character, acting in an immoral manner (κακός), and someone who seeks to involve others in their evil acts (πονηρός) or supports others in their depraved acts (Romans 1:32). All evil comes from unrighteousness (Romans 1:29-31), whether it is done in secret or publicly. And it starts within the mind forming thoughts that work out to doing things that are immoral and are contrary to truth.
As Christians, we are to bring every thought into captivity unto obedience to Christ (2 Corinthians 10:5) while governing our lives by the desires from the Spirit so the cravings from the flesh are never brought to completion (Galatians 5:16). For that bad that we find ourselves doing rather than the good we seek to do (Romans 7:15-20), we need to remember that God imputes Christ death and resurrection to us (Romans 6:3-4), count this to be true (Romans 6:11), and start yielding our members to righteousness (Romans 6:13) so that we fulfill the law of the Spirit of life in Christ Jesus, which sets us free from the law of the sin nature (Romans 8:1-4) and then we are able to do the good (ἀγαθός) things we desire while rejecting the wrong (κακός).