All parts of the human body correspond to spiritual things. That includes the sex organs of both men and women, which correspond to the true love that can exist in a marriage when both the husband and wife are seeking to do the Lord’s will and to be joined to each other internally.
Heaven is filled with that marriage love, and all other loves come from this marriage love -- making it the most important of all human loves.
Since the foreskin covers the male sex organ, then, it represents evil loves that block that marriage love – the love of self and the love of things of the world. Cutting it off represents ridding ourselves of those loves and being purified. This concept is actually relatively clear in the Bible, which also frequently mentions circumcision of the heart and occasionally the circumcision of the lips - getting rid of evil loves and evil speech. In Genesis 17:10, circumcision signifies purity.
