See this explained in Matthew 12:9-13.
Or to do evil? to save life, or to kill? - It seems to have been a maxim with the Jews that not to do good when we have an opportunity is to do evil; not to save life is to kill or to be guilty of murder. If a man has an opportunity of saving a man’s life when he is in danger, and does not do it, he is evidently guilty of his death. On this principle our Saviour puts this question to the Jews - whether it was better for him, having the power to heal this man, to do it, or to suffer him to remain in this suffering condition; and he illustrates it by an example, showing that in a manner of much less importance - that respecting their cattle - they would do on the Sabbath just as “he” would if he should heal this man. The same remark may apply to all opportunities of doing good. “The ability to do good imposes an obligation to do it” (Cotton Mather) He that has the means of feeding the hungry, and clothing the naked, and instructing the ignorant, and sending the gospel to the destitute, and that does it not, is guilty, for he is practically doing evil; he is suffering evils to exist which he might remove. So the wicked will be condemned in the day of judgment because “they did it not,” Matthew 25:45. If this is true, what an obligation rests upon the rich to do good!
With anger - With a severe and stern countenance; with indignation at their hypocrisy and hardness of heart. This was not, however, a spiteful or revengeful passion; it was caused by excessive “grief” at their state: “being grieved for the hardness of their hearts.” It was not hatred of the “men” whose hearts were so hard; it was hatred of the sin which they exhibited, joined with the extreme grief that neither his teaching nor the law of God, nor any means which could be used, overcame their confirmed wickedness. Such anger is not unlawful, Ephesians 4:26. However, in this instance, our Lord has taught us that anger is never lawful except when it is tempered with grief or compassion for those who have offended.
Hardness of their hearts - The heart, figuratively the seat of feeling or affection, is said to be tender when it is easily affected by the sufferings of others - by our own sin and danger - by the love and commands of God; when we are easily made to feel on the great subjects pertaining to our interest, Ezekiel 11:19-20. It is hard when nothing moves it; when a man is alike insensible to the sufferings of others, to the dangers of his own condition, and to the commands, the love, and the threatenings of God. It is most tender in youth, or when we have committed fewest crimes. It is made hard by indulgence in sin, by long resisting the offers of salvation, or by opposing any great and affecting appeals which God may make to us by his Spirit or providence, by affliction, or by a revival of religion. Hence, it is that the most favorable period for securing an interest in Christ, or for becoming a Christian, is in youth the first, the tenderest, and the best days of life. Nay, in the days of childhood, in the Sabbath-school, God may be found, and the soul prepared to die.