The modern understanding of conscience as a faculty by which past actions or dispositions are assessed or future actions evaluated, leading to experiences of guilt or of innocence, is not that of the Bible—though that is not to say that the Bible is unaware of these feelings (cf. 1 Sam. 24: 5).
In the NT human beings are regarded as morally responsible and ‘conscience’ is the painful reaction felt when one's ordered human nature is violated. Conscience therefore is something from which a Christian should be free (Rom. 13: 5); it comes into operation after a wrong deed has been initiated. If there is no such reaction (‘conscience’), then either the deed is not wrong, or habit or environment has so corrupted the subject that ‘conscience’ fails to be activated. ‘Because of conscience’ (Rom. 13: 5) means ‘to avoid the pains of conscience’.
This conscience could lead to excessive scruples on the one hand, or be so insensitive on the other that weaker Christians are hurt (1 Cor. 10: 28).