The Uncleanness of A Man's Natural Emission (Leviticus 15:16-18).
“And if any man's seed of copulation go out from him, then he shall bathe all his flesh in water, and be unclean until the evening. And every garment, and every skin, whereon is the seed of copulation, shall be washed with water, and be unclean until the evening.”
More remarkably a man's natural emissions are seen as rendering the man unclean. For they too are seen as producing imperfect life, life which will die, and as reducing his strength and his ‘perfection'. There is no way here that a man's sexual relationship with a woman can be seen as anything but secular. Far from connecting him with God, it is seen to keep him at a distance. He cannot enter the tabernacle court, nor can he partake of peace offerings on the same day as he engages in sexual relations. So whatever else it is sex is not an aid to spirituality. It is therefore significant that the angels in Heaven do not engage in it, they ‘neither marry nor are given in marriage' (Matthew 22:30).
And as a result of his emission he must wash himself thoroughly and will be unclean until the evening. Note that as ever it is the passage of time that finally cleanses. The washing removed the earthiness and the semen, the passage of time makes clean. (Old Testament ritual washing never cleanses on its own).
Under special circumstances sexual relations have to be abstained from altogether by a man for they prevent his approach to God, and his effectiveness as a soldier of God. See Exodus 19:15; Leviticus 22:4; Deuteronomy 23:10; 1 Samuel 21:4-5; 2 Samuel 11:11. Indeed any time he would approach God in the tabernacle court or partake in peace offerings he must abstain from sexual relations that day..
This view of the semen as being polluted was a regular one outside Canaan, both in Babylon and Egypt and among certain Semites.
“The woman also with whom a man shall lie with seed of copulation, they shall both bathe themselves in water, and be unclean until the evening.”
The same is true for the woman. Once she has had contact with the man's semen she too is unclean until the evening.
It should, however, be noted that these things are not seen as especially unclean. The requirement for their removal is at the lower level, even in the case of the necessary offerings for the unusual emission. We should note here that no offerings are required in respect of normal emissions. They were not seen as sinful in themselves, only as a men and women losing something of their wholeness, and being connected with sin indirectly.