Jesus did not want His critics to gain any satisfaction from what He had just said. Their externally righteous appearance did not excuse them from speaking as they did. Rather people"s words are what God will use to judge them eventually. The "careless" word is the word spoken without deliberation. One might think it insignificant except that it reveals character. Every word spoken reflects the heart"s overflow, and God knows about it. Therefore words are very important (cf. Ephesians 5:3-4; Ephesians 5:12; Colossians 3:17; James 1:19; James 3:1-12). [source][source][source]Matthew 12:37 sounds as though it may have been proverbial, or perhaps Jesus made it a proverb here. The context clarifies that the justification and condemnation in view deal with God passing judgment on everyone. Obviously Jesus did not mean that if a person was able to say all the right words he or she could deceive God and win salvation by clever speech. The basis of justification and condemnation is character, but words reveal character and so become the instruments by which God judges. [source][source][source]
Jesus" critics thought they were assessing Him when they said He did His works by Satan"s power ( Matthew 12:24). Jesus pointed out that they were really assessing themselves. They thought they were judging Him with their words, but really God would judge them with their words. [source][source][source]
The break between Jesus and the religious leaders was now final. [source][source][source]
"It is worth noting that in Mt. the breach between Jesus and the authorities is not definite until the Beelzebub charge." [1][source]