Colin Kruse on the unreliability of conscience

“Seeing that all of human nature has been affected by sin, both a person’s perception of the standard of action required and the function of the conscience itself (as a constituent part of human nature) are also affected by sin. For this reason conscience can never be accorded the position of ultimate judge of one’s behavior. It is possible that the conscience may excuse one for that which God will not excuse, and conversely it is equally possible that conscience may condemn a person for that which God allows. The final judgment therefore belongs only to God (cf. 1 Cor. 4:2-5). Nevertheless, to reject the voice of conscience is to court spiritual disaster (cf. 1 Tim. 1:19). We cannot reject the voice of conscience with impunity, but we can modify the highest standard to which it relates by gaining for ourselves a greater understanding of the truth.”
Colin Kruse
The Second Epistle of Paul to the Corinthians, p. 71.