Leviticus 15:24

If a man lay with her and her uncleanness came upon him, he became unclean for seven days, and the bed upon which he lay became unclean as well. The meaning cannot be merely if he lie upon the same bed with her, but if he have conjugal intercourse, as is evident from Lev 20:18 and Num 5:13 (cf. Gen 26:10; Gen 34:2; Gen 35:22; Sa1 2:22). It cannot be adduced as an objection to this explanation, which is the only admissible one, that according to Lev 18:19 and Lev 20:18 intercourse with a woman during her menses was an accursed crime, to be punished by extermination. For the law in Lev 20:18 refers partly to conjugal intercourse during the hemorrhage of a woman after child-birth, as the similarity of the words in Lev 20:18 and Lev 12:7 (דּמיה מקור) clearly proves, and to the case of a man attempting cohabitation with a woman during her menstruation. The verse before us, on the contrary, refers simply to the possibility of menstruation commencing during the act of conjugal intercourse, when the man would be involuntarily defiled through the unexpected uncleanness of the woman.

In this chapter we have laws concerning other ceremonial uncleannesses contracted either by bodily disease like that of the leper, or some natural incidents, and this either, I. In men (v. 1-18). Or, II. In women (Lev 15:19-33). We need not be at all curious in explaining these antiquated laws, it is enough if we observe the general intention; but we have need to be very cautious lest sin take occasion by the commandment to become more exceedingly sinful; and exceedingly sinful it is when lust is kindled by sparks of fire from God's altar. The case is bad with the soul when it is putrefied by that which should purify it.

15:24 Sexual intercourse with a woman during her menstrual period will later be forbidden and given a harsh penalty (18:19). This verse probably describes a case in which the woman’s menstrual flow went unnoticed when the sexual activity began or in which the woman’s period began during intercourse. The regulations required the man who came into contact with her blood to share the woman’s seven-day quarantine.