Jamieson, Fausset and Brown on Mark 2:7

7. Why doth this man thus speak blasphemies? who can forgive sins but God only?--In this second question they expressed a great truth. (See Is 43:25; Mi 7:18; Ex 34:6, 7, &c.). Nor was their first question altogether unnatural, though in our Lord's sole case it was unfounded. That a man, to all appearances like one of themselves, should claim authority and power to forgive sins, they could not, on the first blush of it, but regard as in the last degree startling; nor were they entitled even to weigh such a claim, as worthy of a hearing, save on supposition of resistless evidence afforded by Him in support of the claim. Accordingly, our Lord deals with them as men entitled to such evidence, and supplies it; at the same time chiding them for rashness, in drawing harsh conclusions regarding Himself.