When you read the Old Testament, consider not the marriages of that time, but the multitude of offspring; not the eating of flesh and the bloody sacrifices, crimes expiated by the death of the flesh, the partnership of many wives permitted to one man. For what was lawful in that time is not lawful in this; and as marriage was granted through the law, so virginity was proclaimed through the Gospel. For the Hebrew nation was separated from all fellowship of peoples, and appointed as a Church for prophesying Christ. Lest it should perish, marriages were permitted to all, for the sake of propagating offspring. And because the people was carnal, it was born of the surfeit of flesh.
Sacrifices of cattle were assuredly offered for this reason, because they prefigured the true sacrifice, that is, the body and blood of Christ. The truth came, the shadow departed; the true sacrifice came, and the victim of cattle ceased. The Virgin's Son came, the Son of a virgin, and gave the proof of virginity. For everything that you read in the Old Testament, although it was done in deed, understand it nevertheless spiritually, and from the truth of the history take the sense of spiritual understanding. Now for sin a man is not slain in the body; but the death which they used to give to that flesh by the sword, we impose upon carnal vices through the practice of penance.
Do not understand the Song of Songs according to the hearing of the ears, because they insinuate the carnal allurement of earthly love, which through the kinds of action figure the love of Christ and the Church. Rightly were these books forbidden by the ancients to be read by carnal persons, that is, the Heptateuch and the Song of Songs: lest, while they do not know them spiritually, they be loosed by the incitement of lust and pleasures.