What counts as a sin in mind is the question of many christian in the world today.
Sin is anything that is contrary to the law or will of God. For example: if you lie, you have sinned. Why? Because God has said not to lie (Ex. 20:16). If you do what God has forbidden, then you have sinned. In addition, if you do not do what God has commanded, you sin (James 4:17). Either way, the result is eternal separation from God (Is. 59:2). Sin is lawlessness (1 John 1:3) and unrighteousness (1 John 5:17). Sin leads to blindness (John 9:41) and death (Rom. 6:23).
Paul, in the book of Romans, discusses sin. He shows that everyone, both Jew and Greek, is under sin (Rom. 3:9). He shows that sin is not simply something that is done, but a condition of the heart (Rom. 3:3,10,11,12). In Ephesians Paul says that we are “by nature children of wrath” (Rom. 2:3). Yet, “while we were still helpless, at the right time Christ died for the ungodly” (Rom. 5:6).
The power of sin is centrifugal. When at work in a human life, it tends to push everything out toward the periphery. Bits and pieces go flying off until only the core is left. Eventually bits and pieces of the core itself go flying off until in the end nothing at all is left. “The wages of sin is death” is St. Paul’s way of saying the same thing.
Other people and (if you happen to believe in him) God or (if you happen not to) the World, Society, Nature—whatever you call the greater whole of which you’re part—sin is whatever you do, or fail to do, that pushes them away, that widens the gap between you and them and also the gaps within your self.
For example, the sin of the Pharisee is not just (a) his holier-than-thou attitude which pushes other people away, but (b) his secret suspicion that his own holiness is deficient too, which pushes part of himself away, and (c) his possibly not-so-subconscious feeling that anybody who expects him to be all that holy must be a cosmic SOB, which pushes Guess Who away.
Sex is counted as sin to the degree that, instead of drawing you closer to another human being in his humanness, it unites bodies but leaves the lives inside them hungrier and more alone than before.
Religion and unreligion are both counts sinful to the degree that they widen the gap between you and the people who don’t share your views.
The word charity illustrates the insidiousness of sin. From meaning a free and loving gift it has come to mean a demeaning handout.
“Original Sin” means we all originate out of a sinful world which taints us from the word go. We all tend to make ourselves the center of the universe, pushing away centrifugally from the center everything that seems to impede its freewheeling. More even than hunger, poverty, or disease, it is what Jesus said he came to save the world from.