Sin is anything that comes between us and God.
Sin prevents our being open to receive God's grace and love.
Sin is a cause of great loss to us and of sorrow to God.
Almost anything can be a sin (even playing football on a Sunday morning instead of going to church - if it comes between us and God), and some actions (such as stealing or murder) are almost always sinful.
One good test of whether something is sinful or not is to ask whether it causes us to break one of the great commandments - see Matthew 22.34, Mark 12.30, and Luke 10.27.
Another way of talking about sin is to say that on account of sin we become alienated from God.
The remedy for sin (the antidote to sin) is penitence and repentance. Through the death of Christ on the cross, we may be restored to God's favour.
© J D Yule 2003