The heart represents the seat of feeling and affection. For instance, one is said to be tenderhearted when easily affected by others' sufferings. A person may be affected by his own sin or, in contrast, by the love and commands of God. The Pharisees act, not with sorrowful indignation, but with ruthless, murderous hearts (Mark 3:6). While theirs were hardened, Jesus' heart ached. What a contrast!
Here is illustrated the nadir of the Pharisees' hypocrisy. They policed Sabbath activities to ensure no one broke their human rules for keeping it, condemning those who did, while having no qualms about plotting Jesus' murder! They would allow the rescue of a sheep on the Sabbath but not the rescue—through healing—of a human being.
God prophesies about the church:
Then I will give them one heart, and I will put a new spirit within them, and take the stony heart out of their flesh, and give them a heart of flesh, that they may walk in My statutes and keep My judgments and do them; and they shall be My people, and I will be their God. (Ezekiel 11:19-20)
The day will come when we will all have "a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience and our bodies washed with pure water" (Hebrews 10:22). As the next verse encourages, "He who promised is faithful." He will create this clean heart in us as we follow the righteous example of His Son.