What does the Holy Bible say about thoughts being a sin?

Answer 1

A person goes bad because he lets his own selfish reasoning, his own ambitions and desires, his chosen associates and surroundings, mold his thinking and determine the direction of his will. Paul spoke of some who were ‘once enlightened, had tasted the heavenly free gift, but had fallen away.’ (Hebrews 6:4-6) If we are not continually on guard, the Devil can by his sly propaganda make our hearts receptive to apostate thinking.  Unclean and immoral worldly thinking can ruin even the mature Christian. No one is immune to temptation. All must fight the sinful tendencies of the flesh and avoid things that whip up fleshly desires. It is wise, therefore, to heed the counsel from God’s Word: “Do not be misled. Bad associations spoil useful habits.” (1 Cor. 15:33) That means avoiding the company of those without faith, persons of evil or perverted inclinations, desires or conduct​—fornicators, adulterers, homosexuals, drunkards and sadists. Would it not also include keeping them out of one’s thoughts by not meditating on such types, by not reading about them for sensual pleasure, by not viewing them for entertainment on the television screen or on a motion-picture screen? Likewise, the use of vulgar speech and the telling of obscene jokes and stories, which many worldlings consider “adult” conduct, would be weakening to mature Christians and detrimental to those seeking to attain Christian maturity. Such things should be shunned, as God’s Word counsels: “Let fornication and uncleanness of every sort or greediness not even be mentioned among you, just as it befits holy people; neither shameful conduct nor foolish talking nor obscene jesting, things which are not becoming.”​—Eph. 5:3, 4; 4:29-31; Col. 3:5-10. To desire another person’s marriage mate is a sin. (Deuteronomy 5:21) If a Christian begins to have this desire, he or she should quickly do everything possible to remove that unclean desire from his or her mind.Bible writer James said about wrong desires and what they lead to. “But each one is tried by being drawn out and enticed by his own desire. Then the desire, when it has become fertile, gives birth to sin; in turn, sin, when it has been accomplished, brings forth death.” (Jas. 1:14, 15, NW)