Karl Barth describes sin in three ways, each in relation to an aspect of the work of Christ:
1. Where Christ humbled himself, each and every other human being exalts himself. This is all the more striking when we bear in mind the inherent glory of Christ as the Image and Son of God, and on the other hand the dust from which humanity is shaped. Despite this, Christ humbled himself to death - even death on a cross, in striking contrast to the status-seeking and self-promotion of humanity. Sin in its first form is pride.
2. Where Christ obeyed God and lived a life of active fellowship with him, each and every other human being avoids God's call and resists his fellowship. Jesus always did the will of his Father, even when that will led him to Calvary. We, on the other hand, do not respond to God's call. We do not take up the responsibility of living toward God, but instead fall for the lure of irresponsibility and inaction. Sin in its second form is sloth.
3. Where Christ bore true witness to God, each and every other human being distorts or ignores the knowledge of God. Jesus was the light of the world, but we prefer to live in darkness. We manufacture idols, literal or metaphorical, and create gods in our own image. In doing so, we lose touch with ultimate truth, and consequently with all truth. Sin in its third form is falsehood.
Obviously this is not the only way to think about sin, but I find it helpful especially for the way it places our sin in the context of Christ's righteousness. Here, face to face with the only example of human righteousness there has ever been, we are surely forced to acknowledge that we not only fall short but set off in entirely the wrong direction.
Kyrie eleison. Christe eleison.