Albert Barnes on Luke 6:8

But he knew their thoughts. He knew their thoughts--their dark, malicious designs--by the question which they proposed to him, whether it was lawful to heal on the Sabbath-days (Matthew). In reply to their question, Jesus asked them whether they would not release a sheep on the Sabbath-day if it was fallen into a pit, and also asked them whether it was better to do good than to do evil on that day, implying that to omit to do good was, in fact, doing evil.

(g) "But he knew their thoughts" Job 42:2