External behavior is not an accurate gauge of your character. The thoughts of your heart, only known to God and your conscience, reveal the truth.

It is so crucial that we cultivate a pure life so that we can enjoy the testimony of a clear conscience. The longer you learn the Word, the more you’re exposed to the Word, the more your heart is filled with its truth, the greater will be your love and your worship toward God. I honestly don’t know how men can possibly feed their thought life with filth, foul things, obscenities, and things which displease God, and stand and minister without being assaulted by their conscience.

Job’s comforters came to him and falsely accused him, and there wasn’t anything in his life they could accuse him of. You remember Job? He was more righteous than any other man, so what were they going to accuse him of? They accused him of a dirty thought life. Zophar came and said this to him:

Though evil is sweet in his mouth
And he hides it under his tongue,
Though he desires it and will not forsake it,
And holds it to his palate. (Job 20:12-13)

You don’t see it, and you don’t hear it, but he’s all foul on the inside. The picture he painted of the evil thinker is vividly true. Evil thoughts are like candy to them.They derive great satisfaction from their imaginary iniquities. They savor their evil fantasies. They relish them like a choice morsel of sweetness under their tongue. They return to the same wicked musings from which they can glean illicit pleasure over and over again. They mull them over like an animal chewing the cud, bringing up the favorite evil thoughts time and time again to react anew in the mind.

This is what they accused Job of. But they had misjudged him.

Job had carefully guarded himself against that. This is what he said in Job 31:1:

I have cut a covenant with my eyes;
How then could I gaze at a virgin?

He says, “I don’t look in any direction that’s going to cultivate an evil thought.” He knew God was the audience to his thoughts. He says this: “Does He not see my ways and number all my steps? If I have walked with falsehood and my foot has hastened after deceit, let Him weigh me with just scales and let God know my integrity.” And then Job denied that his heart had followed his eyes, that his heart had been enticed by another woman. That would be a lustful crime, he says, and to hide iniquity in the bosom would be to cover one’s transgression like Adam. The very thought appalled his righteous heart.

No, Job was very aware of the danger of sinful thoughts. He consciously, deliberately set a guard on his heart to avoid such things. He even offers a sacrifice to God just in case his children sinned in their hearts:

Now it happened when the days of feasting had completed their cycle, that Job would send and set them apart as holy. And he would rise up early in the morning and offer burnt offerings according to the number of them all; for Job said, “Perhaps my sons have sinned and cursed God in their hearts.” Thus Job did continually. (Job 1:5)

He was concerned not only about his own thought life, but the thought life of his own family. That’s why the Lord said there’s no one like him on the earth. He’s a blameless and upright man.

So, this whole matter of sins of thought has to be dealt with if we’re going to liberate our conscience and enjoy peace and joy and happiness and bliss in the Christian experience. If you want to quiet your noisy conscience, you’ve got to deal with your thought life.

This post is based on a sermon Dr. MacArthur preached in 1994, titled “Keeping a Pure Mind.” In addition to serving as the pastor of Grace Community Church and the voice of Grace to You, Dr. MacArthur is the chancellor of The Master’s University in Santa Clarita, Calif. You can learn more about TMU at www.masters.edu.