Sin leading to death 

The Bible clearly teaches there are 2 kinds of sin: venial and mortal. Committing mortal sins causes us to lose our salvation because it separates us from God. God cannot look upon these sins.

The 10 commandments provides a list of mortal sins.

The common teaching that a little white lie is as bad as murder is simply mistaken. All sin repels us away from God's presence. The worse the sin, the stronger the repulsion and the more difficult for the soul to finally accept redemption when offered.

Many places in the New Testament contain lists of mortal sins. Notice how horrible these are and, what is weird, apparently these were very common of the Christians of the day. I suppose that's why the Churches of Revelation got such bad reviews.

People who spend large amounts of time agonizing over small character flaws often do so based on the faulty teaching that we are totally depraved; deserving of hell from birth. But Adam and Eve were created in God's image and some of this goodness persists; we are tainted by original sin but God's grace still moves in us prompting us to do good and reject evil. Certainly this is easier after being indwelt of the Holy Spirit through faith in Christ.