John Lightfoot on Mark 12:28

[Which is the first commandment of all?] It is not seldom that this distinction occurs in the Rabbins, between the law, and the precept: by the latter they understand some special or greater rite (themselves being judges); such as circumcision, the repeating of the phylacteries, keeping the sabbath, &c. This question, propounded by the scribe, seems to respect the same: namely, whether those great precepts (as they were esteemed) and other ceremonial precepts of that nature, such as sacrifices, purifications, keeping festivals, were the greatest precepts of the law, or no: and if it were so, which among them was the first?

By his answer he seems to incline to the negative, and to prefer the moral law. Whence Christ saith, "That he was not far from the kingdom of heaven": and while he suits an answer to him from that very passage, which was the first in the reciting of the phylacteries, Hear, O Israel,--he directs the eyes and the minds of those that repeated them to the sense and the marrow of the thing repeated,--and that they rest not in the bare work of repeating them.