Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
The following commentary covers Chapters 11 and 12.
Priesthood being established, there comes the discernment between holy things and profane, and the judgment of defilements (chaps. 11-15), and what was to be done for the purification of defiled persons. We see that it is this nearness of separation unto God which alone can discern thus, and such is the service and ever the duty of priests.
First, as to food, that which is allowed to be eaten. In general the principle seems to be, that anything is allowed that is clean, in this sense, first, that it is thoroughly according to its element, that is, in principle, divine order (of course here presented in a figure), as fishes having scales; secondly, that was allowed which united mature digestion to the absence of that wilful energy which goes boldly through everything. These two qualities must be united. The grossness which swallows down things as they are, or the lack of quiet firmness, rendered unclean. To be clean, it must be that which at the same time chews the cud and divides the hoof. Of birds, the carnivorous night birds and those which cannot be tamed are forbidden; creeping things also, whatever grovelled and trailed itself on the earth. In general, there was to be in their eating the discernment of what was clean.
Then we have the judgment of God fallen on that which would have been, for unfallen man, joy and blessing. The birth of a man, connected now with sin, renders unclean; that of a woman, in whom was the transgression, being deceived, still more so [See Note #1].
Note #1
Connected with this was the weakness of fallen nature (compare Gen 1:2). All that belonged even to weakness of nature, being the effect of sin, rendered unclean under the law. This is also true spiritually. All this was the result of some manifestation or other of the life that was in the flesh. It was so with the leper; raw flesh rendered unclean, as well as any other case where this life (which had become unclean, and had been as set aside and under judgment through sin), manifested itself externally, even though weakness alone were the cause of its manifestation.