The Reply to the Third Objection is clear from what has been said (ad 1).

Reply Obj. 4:  Although the kid that is slain has no perception of the manner in which its flesh is cooked, yet it would seem to savor of heartlessness if the dam’s milk, which was intended for the nourishment of her offspring, were served up on the same dish.  It might also be said that the Gentiles in celebrating the feasts of their idols prepared the flesh of kids in this manner, for the purpose of sacrifice or banquet:  hence (Ex. 23) after the solemnities to be celebrated under the Law had been foretold, it is added:  “Thou shalt not boil a kid in the milk of its dam.”  The figurative reason for this prohibition is this:  the kid, signifying Christ, on account of “the likeness of sinful flesh” (Rom. 8:3), was not to be seethed, i.e. slain, by the Jews, “in the milk of its dam,” i.e. during His infancy.  Or else it signifies that the kid, i.e. the sinner, should not be boiled in the milk of its dam, i.e. should not be cajoled by flattery.

Reply Obj. 5:  The Gentiles offered their gods the first-fruits, which they held to bring them good luck:  or they burnt them for the purpose of secrecy.  Consequently (the Israelites) were commanded to look upon the fruits of the first three years as unclean:  for in that country nearly all the trees bear fruit in three years’ time; those trees, to wit, that are cultivated either from seed, or from a graft, or from a cutting:  but it seldom happens that the fruit-stones or seeds encased in a pod are sown:  since it would take a longer time for these to bear fruit:  and the Law considered what happened most frequently.  The fruits, however, of the fourth year, as being the firstlings of clean fruits, were offered to God:  and from the fifth year onward they were eaten.

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.