What people mean by thought crime
The phrase "thought crime" is not a biblical term. People often use it for the idea that private thoughts alone should be punished, especially when no action has taken place. That can sound frightening, particularly for someone who has distressing or unwanted thoughts.
Scripture takes inner life seriously. God chose David as king when others looked at outward appearance, because God sees the heart (1 Samuel 16:7). Jesus also taught that anger, contempt, lust, and hatred are not harmless simply because they are hidden. They reveal something going on beneath outward behaviour (Matthew 5:22, Matthew 5:28).
But the Lord said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for the Lord seeth not as man seeth; for man looketh on the outward appearance, but the Lord looketh on the heart.
A passing thought is not the same as chosen sin
That does not mean every dark, strange, angry, sexual, or blasphemous thought is a sin. Thoughts can arise from fear, stress, memories, temptation, or a mind that is simply tired. Jesus himself was tempted in the wilderness, yet he did not sin (Hebrews 4:15). Temptation met with resistance is not the same thing as consenting to it.
The Bible's concern is not with demanding impossible mental perfection. It speaks of desires that are welcomed and allowed to grow. James describes temptation becoming sin when desire conceives, then eventually producing sinful action (James 1:14-15). There is a real difference between a thought knocking at the door and choosing to invite it in.
For we have not an high priest which cannot be touched with the feeling of our infirmities; but was in all points tempted like as we are, yet without sin.
Why the heart still matters
Jesus was not lowering the standard of goodness to external rule-keeping. A person may avoid an outward act while feeding resentment, pride, or exploitation inwardly. God cares about the whole person, including motives and desires. That is searching, but it is also honest.
So a biblical answer is more careful than either extreme. It is not true that private thoughts never matter. Nor is it true that God condemns people for every involuntary mental flash. He knows what is deliberate, what is resisted, and what is wounded or troubled within us (Psalm 139:23-24).
Search me, O God, and know my heart: try me, and know my thoughts: And see if there be any wicked way in me, and lead me in the way everlasting.
What to do with troubling thoughts
When you notice a thought that pulls you away from love, truth, or faithfulness, don't panic and don't pretend it is not there. Bring it to God. Paul urged believers to take thoughts captive in obedience to Christ, and to set their minds on what is true, honourable, just, pure, lovely, and worthy of praise (2 Corinthians 10:5, Philippians 4:8). This is a repeated practice, not a one-time test you either pass or fail.
If you have deliberately held onto a sinful attitude, confession is a safe place to begin. God promises forgiveness and cleansing to those who confess (1 John 1:9). If the thoughts are intrusive, relentless, or leave you frightened, talking with a trusted pastor, doctor, counsellor, or someone who knows you well can help. You are not defined by every thought that enters your mind.