"...abhor what is evil; cling to what is good" (Romans 12:9).
This short verse (actually, it is just the second part of the verse) would be a fine one to commit to memory. It states or implies at least three vital points.
First, there is such a thing as good and evil. People used to understand that. We used to know that one is supposed to keep his word, that greed is a bad thing, that marriage is for life, that homosexuality is a perversion, etc. Now, several generations have grown up listening to denominational preachers say that it does not matter what you believe, thereby undermining Bible authority.
We have heard libertarians rationalize any and every kind of conduct. We have grown accustomed to comedians making daily fodder of sin of every kind. Is it any wonder people are confused? Come to think of it, this is nothing new. Long ago Isaiah wrote, "Woe to those who call evil good, and good evil; who substitute darkness for light and light for darkness; ...who are wise in their own eyes and clever in their own sight" (Isaiah 5:20-21).
Second, it is both possible and necessary to discern good and evil. Personal preferences and moral relativism leave us adrift. There is a fixed standard. It is God. He is right or righteous. "A God of faithfulness and without injustice, righteous and upright is He" (Deuteronomy 32:4). His word, His self-revelation, is the yardstick by which all conduct is measured. It is the standard by which we shall be judged (John 12:48).
Discerning right and wrong begins with the "thou shalt/thou shalt not" passages. We must also take into account principles of conduct, such as maintaining a clear conscience (Romans 14:22-23), not putting other things before God (Matthew 6:33), leaving off questionable things that would lessen our influence for good (Matthew 5:16), etc. Paul often prayed that Christians would grow in this area of distinguishing conduct (Philippians 1:9-11; Colossians 1:9-12).
Third, we must act in keeping with the quality of any given behavior. If a thing is good we are to cling to it. The original verb in our text is from the Greek noun for glue; be glued to it. On the other hand, if conduct is bad, we are to abhor it. Abhor is from the Latin word for horror, which literally means to shudder. We should shudder at the very idea of some kinds of behavior [misbehavior].
Simply put, Romans 12:9 tells us to use God's word and draw the line between good and evil. Once that line is drawn, do not see how close to it you can get without stepping over; stay as far away from evil and as close to God as you can.