The figurative reason was that this foreshadowed the fact that after the three states of the Law (the first lasting from Abraham to David, the second, until they were carried away to Babylon, the third until the time of Christ), the Fruit of the Law, i.e. Christ, was to be offered to God. Or again, that we must mistrust our first efforts, on account of their imperfection.
Reply Obj. 6: It is said of a man in Ecclus. 19:27, that "the attire of the body . . . " shows "what he is." Hence the Lord wished His people to be distinguished from other nations, not only by the sign of the circumcision, which was in the flesh, but also by a certain difference of attire. Wherefore they were forbidden to wear garments woven of woolen and linen together, and for a woman to be clothed with man's apparel, or vice versa, for two reasons. First, to avoid idolatrous worship. Because the Gentiles, in their religious rites, used garments of this sort, made of various materials. Moreover in the worship of Mars, women put on men's armor; while, conversely, in the worship of Venus men donned women's attire. The second reason was to preserve them from lust: because the employment of various materials in the making of garments signified inordinate union of sexes, while the use of male attire by a woman, or vice versa, has an incentive to evil desires, and offers an occasion of lust. The figurative reason is that the prohibition of wearing a garment woven of woolen and linen signified that it was forbidden to unite the simplicity of innocence, denoted by wool, with the duplicity of malice, betokened by linen. It also signifies that woman is forbidden to presume to teach, or perform other duties of men: or that man should not adopt the effeminate manners of a woman.
Reply Obj. 7: As Jerome says on Matt. 23:6, "the Lord commanded them to make violet-colored fringes in the four corners of their garments, so that the Israelites might be distinguished from other nations." Hence, in this way, they professed to be Jews: and consequently the very sight of this sign reminded them of their law.
When we read: "Thou shalt bind them on thy hand, and they shall be ever before thy eyes [Vulg.: 'they shall be and shall move between thy eyes'], the Pharisees gave a false interpretation to these words, and wrote the decalogue of Moses on a parchment, and tied it on their foreheads like a wreath, so that it moved in front of their eyes": whereas the intention of the Lord in giving this commandment was that they should be bound in their hands, i.e. in their works; and that they should be before their eyes, i.e. in their thoughts. The violet-colored fillets which were inserted in their cloaks signify the godly intention which should accompany our every deed. It may, however, be said that, because they were a carnal-minded and stiff-necked people, it was necessary for them to be stirred by these sensible things to the observance of the Law.
Reply Obj. 8: Affection in man is twofold: it may be an affection of reason, or it may be an affection of passion. If a man's affection be one of reason, it matters not how man behaves to animals, because God has subjected all things to man's power, according to Ps. 8:8: "Thou hast subjected all things under his feet": and it is in this sense that the Apostle says that "God has no care for oxen"; because God does not ask of man what he does with oxen or other animals.
But if man's affection be one of passion, then it is moved also in regard to other animals: for since the passion of pity is caused by the afflictions of others; and since it happens that even irrational animals are sensible to pain, it is possible for the affection of pity to arise in a man with regard to the sufferings of animals. Now it is evident that if a man practice a pitiful affection for animals, he is all the more disposed to take pity on his fellow-men: wherefore it is written (Prov. 11:10): "The just regardeth the lives of his beasts: but the bowels of the wicked are cruel." Consequently the Lord, in order to inculcate pity to the Jewish people, who were prone to cruelty, wished them to practice pity even with regard to dumb animals, and forbade them to do certain things savoring of cruelty to animals. Hence He prohibited them to "boil a kid in the milk of its dam"; and to "muzzle the ox that treadeth out the corn"; and to slay "the dam with her young." It may, nevertheless, be also said that these prohibitions were made in hatred of idolatry. For the Egyptians held it to be wicked to allow the ox to eat of the grain while threshing the corn. Moreover certain sorcerers were wont to ensnare the mother bird with her young during incubation, and to employ them for the purpose of securing fruitfulness and good luck in bringing up children: also because it was held to be a good omen to find the mother sitting on her young.
As to the mingling of animals of divers species, the literal reason may have been threefold. The first was to show detestation for the idolatry of the Egyptians, who employed various mixtures in worshipping the planets, which produce various effects, and on various kinds of things according to their various conjunctions. The second reason was in condemnation of unnatural sins. The third reason was the entire removal of all occasions of concupiscence. Because animals of different species do not easily breed, unless this be brought about by man; and movements of lust are aroused by seeing such things. Wherefore in the Jewish traditions we find it prescribed as stated by Rabbi Moses that men shall turn away their eyes from such sights.
The figurative reason for these things is that the necessities of life should not be withdrawn from the ox that treadeth the corn, i.e. from the preacher bearing the sheaves of doctrine, as the Apostle states (1 Cor. 9:4, seqq.). Again, we should not take the dam with her young: because in certain things we have to keep the spiritual senses, i.e. the offspring, and set aside the observance of the letter, i.e. the mother, for instance, in all the ceremonies of the Law. It is also forbidden that a beast of burden, i.e. any of the common people, should be allowed to engender, i.e. to have any connection, with animals of another kind, i.e. with Gentiles or Jews.
Reply Obj. 9: All these minglings were forbidden in agriculture; literally, in detestation of idolatry. For the Egyptians in worshipping the stars employed various combinations of seeds, animals and garments, in order to represent the various connections of the stars. Or else all these minglings were forbidden in detestation of the unnatural vice.
They have, however, a figurative reason. For the prohibition: "Thou shalt not sow thy field with different seeds," is to be understood, in the spiritual sense, of the prohibition to sow strange doctrine in the Church, which is a spiritual vineyard. Likewise "the field," i.e. the Church, must not be sown "with different seeds," i.e. with Catholic and heretical doctrines. Neither is it allowed to plough "with an ox and an ass together"; thus a fool should not accompany a wise man in preaching, for one would hinder the other.