Some good quotes on sin:
“The sinner is therefore someone who goes against nature, and it is the nature of human beings to live rationally. Sin is therefore something which must be regarded as absurd” (Theophylact of Ohrid, Byzantine Archbishop, c. 1000 A.D.)
“It is not a speculation but a description which even the veriest child can understand simply to say of evil in the first instance that it is what God does not will. But to say this is also to say that it is something which He never did nor could will, nor ever will nor can. It is thus that evil is characterized, judged, and condemned in the self-disclosure of the living person of Jesus Christ. As opposition to God, it is that which is simply opposed to His will, and from eternity, in time and to all eternity negated, rejected, condemned and excluded by his will.” (Karl Barth, Curch Dogmatics IV/3, 1:177)