All humans are sinners. Some are saved by grace, and others aren't. But all humans have the same mechanism to help restrain sin in their lives: the conscience.
Our conscience is part of a person's internal rational capacity and is not, as popular lore sometimes suggests, an audience room for the voice of God or of the devil. Conscience is a critical inner awareness that bears witness to the norms and values we recognize and apply. ~Baker's Evangelical Dictionary of Biblical Theology - ConscienceAs an unsaved person I'd often wonder why it was that everyone knows not to murder another person. All cultures decry murder, and have since the beginning, no matter how 'prehistoric' that culture was. People know not to steal something from another person. Everyone knows not to abuse babies. Everyone everywhere at all eras speaks of the concepts of 'good' and 'evil.'
Why is it that humans all similarly have an innate moral compass? Why don't animals?
It's because God gave us a conscience. The Bible speaks a lot about the conscience. Here are just a few!
And your ears shall hear a word behind you, saying, “This is the way, walk in it,” when you turn to the right or when you turn to the left. (Isaiah 30:21)
They show that the work of the law is written on their hearts, while their conscience also bears witness, and their conflicting thoughts accuse or even excuse them. (Romans 2:15)
Let us draw near with a true heart in full assurance of faith, with our hearts sprinkled clean from an evil conscience and our bodies washed with pure water. (Hebrews 10:22)
The aim of our charge is love that issues from a pure heart and a good conscience and a sincere faith. (1 Timothy 1:5)
Holding faith and a good conscience. By rejecting this, some have made shipwreck of their faith, (1 Timothy 1:19).
I liked the Isaiah verse, it was so descriptive of how the conscience works. It doesn't mean to actually hear a voice. Refer back tot he definition above. It just means that we hear and feel an alert when something is awry with our moral compass. The compass dial is spinning. It's a warning signal not to do something 'evil', or, if we already did, that it was wrong to do so.
Our automobiles come with a lot of electronics these days. One of them is a system on the dashboard that lights up a warning light. When the 'check engine' light comes on, you know something is wrong in the engine!
My father hated the check engine light. He didn't want anyone to 'tell him what to do'. So if a dashboard light came on he'd put black electrical tape over it.
Do we do that with our conscience? If we do, it is a dangerous thing to do. When we ignore the conscience long enough, it might get seared.
Speaking lies in hypocrisy; having their conscience seared with a hot iron; (1 Timothy 4:2)
Having their conscience seared with a hot iron - The allusion here is doubtless to the effect of applying a hot iron to the skin. The cauterized part becomes rigid and hard, and is dead to sensibility. So with the conscience of those referred to. ~Barnes Notes
And, as the Jamieson-Fausset-Brown Bible Commentary says, the result of ignoring the warnings of the conscience not only leads to a seared conscience, but to hypocrisy-
Bad consciences always have recourse to hypocrisy. As faith and a good conscience are joined (1Ti 1:5); so hypocrisy (that is, unbelief, Mt 24:5, 51; compare Lu 12:46) .Don't ignore, or worse block out the warning signs of the conscience by covering it over. The conscience is a grace given to us by God. After salvation, we have an additional mechanism to help us resist sin- the Holy Spirit, He pricks our conscience.
If you are righteous, honorable, and good because your conscience responds to God's commands, it is a good conscience. But if you are doing good works or religious ritual just so that others will see, those are not from a good conscience (Matt. 6:5-6, 16–18). A good conscience holds us accountable simply because God commands it. The conscience is God's deputy in the heart of a believer.
Therefore what we do from a good conscience we do from the heart. When we do something grudgingly, not out of love, and not from the heart, that is not from a good conscience. A healthy conscience looks not merely to what we do, but it examines why we do it as well—whether it is out of love for God and a desire to obey, or from a sense of resentful obligation.
A good conscience renounces and denies all sin. Those, therefore, who labor to feed their corruptions while thinking they are Christians contradict their profession of faith. ~The Vanishing Conscience, By John F. MacArthurSo, I guess that's about it. Is your 'check engine' light on? If it is, have you responded to it appropriately? Our Savior is so forgiving, if you approach the throne of grace, repentantly, He will forgive! For the Christian, it is not a throne of judgment. It is a throne of love and kindness, of a Father to His children. You can always include in your prayers an appeal to the Spirit to keep your conscience sharp and active, not let it get seared with overlays of unaddressed sin. I know I will.