SIN AS not-TRUST?

In his book, Sickness Unto Death, Soren Kierkegaard makes the point that the opposite of sin is faith (trust). At first read, this took me off guard, for sin seems to be primarily a set of behaviors and attitudes rather than a lack of trust. Romans 14:20-23, "For whatever does not proceed from faith is sin," seems to confirm Kierkegaard's notion; therefore, this idea requires further consideration.

I went back to King David and how God called him a man after God's heart despite his being an adulterer and a murderer (1 Kings 11:4; Acts 13:22). These two sins--adultery and murder--are certainly behaviors with accompanying attitudes and they are certainly sin. On the other hand, neither having relations with a woman nor killing a human is necessarily sin. It is not these specific behaviors, but rather other factors that make these behaviors to be sin.

Following Kierkegaard's notion of sin as not-trust, can it be shown that lack of trust is the key factor that determines whether or not a specific behavior or attitude is sin?

Tag(s): kierkegaard spiritual formation