A selection of verses showing that our bad thoughts are as bad as our deeds or can lead to bad deeds.
Jesus reminds his followers that bad thoughts are as bad as the deed in his teaching on the mount in Matthew 5:
21 “You have heard that it was said to the ancient ones, ‘You shall not murder;’ and ‘Whoever murders will be in danger of the judgement.’ 22 But I tell you that everyone who is angry with his brother without a cause will be in danger of the judgement. Whoever says to his brother, ‘Raca!’ will be in danger of the council. Whoever says, ‘You fool!’ will be in danger of the fire of Gehenna.
27 “You have heard that it was said, ‘You shall not commit adultery;’ 28 but I tell you that everyone who gazes at a woman to lust after her has committed adultery with her already in his heart.
The apostle Paul tells Timothy that wanting to be rich can lead to all kinds of bad actions:
9 But those who are determined to be rich fall into a temptation, a snare, and many foolish and harmful lusts, such as drown men in ruin and destruction. 10 For the love of money is a root of all kinds of evil. Some have been led astray from the faith in their greed, and have pierced themselves through with many sorrows.
The apostle John tells us that hating our brother is as bad as murdering him:
14 We know that we have passed out of death into life, because we love the brothers. He who doesn’t love his brother remains in death. 15 Whoever hates his brother is a murderer, and you know that no murderer has eternal life remaining in him.
The apostle James tells us that strife comes from our desires:
1 Where do wars and fightings amongst you come from? Don’t they come from your pleasures that war in your members? 2 You lust, and don’t have. You murder and covet, and can’t obtain. You fight and make war. You don’t have, because you don’t ask. 3 You ask, and don’t receive, because you ask with wrong motives, so that you may spend it on your pleasures.