Note 18 at 1 Tim. 1:19: The conscience is the self-judging function of the heart that either accuses or excuses one's self in regard to his conduct (see note 9 at Rom. 2:15 p. 750). It is the faculty that recognizes right from wrong and demands that one do right and avoid doing wrong. Although it is true that the conscience is not infallible and can make mistakes (Rom. 14:2), we cannot ignore it and succeed. We must have a good conscience to see our faith reach its goal (see note 19 at this verse).

There are two ways of maintaining a good conscience, which are equally important. We cannot depend on one alone. First, it is the blood of Jesus that purges our conscience (Heb. 9:14). Regardless of what we have done in the past or might do in the future, God's blood has cleansed us from all our sins (see note 11 at Rom. 4:8, p. 762). We need to appropriate that cleansing for our conscience.

Many people think, "That ought to do it, what else do I need besides the blood of Jesus?" We also need to stop defiling our conscience as much as possible. If a person just flagrantly lives in sin because he is forgiven, then tries to purge his conscience, it won't work. Your conscience can only be cleansed of "dead" works (Heb. 9:14). That means works that are in the past. Every time anyone commits a sin his conscience will condemn him afresh.

So, anyone who thinks he can live in a constant state of sin with no harmful effects is ignoring his conscience. God may still love you, but your own heart will condemn you and rob you of confidence (1 Jn. 3:19-21). Your faith will become shipwrecked and never reach its goal. (For more information on the conscience see note 2 at 1 Cor. 8:1, p. 898: note 12 at 1 Cor. 8:7, p. 900; note 15 at 1 Cor. 8:10, p. 901; notes 1-2 at 2 Cor. 1:12, p. 979; note 1 at Acts 23:1, p. 709; note 4 at Acts 24:16, p. 716; note 56 at Jn. 15:10, p. 495).

Note 19 at 1 Tim. 1:19: By failing to maintain a good conscience, some have shipwrecked their faith. "Shipwreck" indicates destruction by a storm or collision. It depicts a ship that left, but never arrived at its destination. Likewise, we not only need to start in faith, but maintain that faith until it brings us to the desired result.

To keep our faith on course and avoid a shipwreck, Paul said we must have a good conscience. As discussed in the previous footnote at this verse, that is done through the combination of not defiling our consciences as much as possible and then using the blood of Jesus to cleanse away any condemnation from past sins and failures.