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!

To do good - or - evil? to save life, or to kill? - It was a maxim with the Jews, as it should be with all men, that he who neglected to preserve life when it was in his power, was to be reputed a murderer. Every principle of sound justice requires that he should be considered in this light. But, if this be the case, how many murderers are there against whom there is no law but the law of God!
To kill - but instead of αποκτειναι, several MSS. and versions have απολεσαι to destroy. Wetstein and Griesbach quote Theophylact for this reading; but it is not in my copy. Paris edit. 1635.

And he saith unto them, Is it lawful to do good on the sabbath days, or to do evil? to save (b) life, or to kill? But they held their peace.
(b) He uses here the figure of speech called synecdoche, for this type of saying, "to save the life", is the same as saying "to save the man".

And he saith unto them,.... Either to the whole multitude, to all the assembly in the synagogue; and so the Persic version renders it, "again he said to the multitude"; or rather, to the Scribes and Pharisees, who were watching him, and had put a question to him, which he answers by another:
is it lawful to do good on the sabbath days, or to do evil, to save life, or to kill? The Vulgate Latin, Syriac, Arabic, and Persic versions read, or "to destroy", as in Luke 6:9, To do evil, kill, or destroy, are not lawful at any time; and to do good, and to save life, must be right at all times: our Lord has a particular view to the Scribes and Pharisees, and the question is put home to their own consciences; whose hearts and thoughts, designs and views, were all open to Christ; and who were now watching to do evil to him, and even to destroy and take away his life: for the violation of the sabbath was death by the law, and this was what they sought to accuse him of: now he puts the question to them, and makes them judges which must appear most right and just in the sight of God and men, for him to heal this poor man of his withered hand, though on the sabbath day; which would be doing a good and beneficent action to him, whereby his life would be saved, and preserved with comfort and usefulness, and he would be in a capacity of getting his livelihood; or for them to cherish an evil intention against him, to seek to bring mischief on him; and not only destroy his character and usefulness as much as in them lay, but even take away his very life also: he leaves it with them to consider of which was most agreeable to the law of God, the nature of a sabbath, and the good of mankind;
but they held their peace; or "were silent", not being able to return an answer, but what must have been in his favour, and to their own confusion, and therefore chose to say nothing.

Is it lawful . . . to save life, or to kill? A home thrust at the fault-finders. They were harboring murderous thoughts; he was seeking to save life. Which was breaking the Sabbath?

Is it lawful to save life or to kill? - Which he knew they were seeking occasion to do. But they held their peace - Being confounded, though not convinced.