Despite G‑d’s promise, Abraham and his wife Sarah had not yet had any children. Sarah therefore asked her Egyptian bondwoman, Hagar, to bear a child by Abraham, hoping that in this merit she would also conceive. Hagar indeed quickly conceived. Concluding from this that her spiritual merits were greater than her mistress’s, Hagar mocked Sarah, who then told Abraham to send her away. Hagar gave birth to Abraham’s first son, Ishmael. Thirteen years later, G‑d told Abraham that the time had arrived for him to have a son with Sarah, and in preparation for this, he should circumcise himself.
Circumcising Negativity
בְּעֶצֶם הַיּוֹם הַזֶּה נִמּוֹל אַבְרָהָם וגו': (בראשית יז:כו)
On that day, Abraham was circumcised. Genesis 17:26

Spiritually, circumcision is the removal of the “foreskin of the heart,” the layer of apathy and haughtiness that obstructs our true connection with G‑d. In order to spiritually circumcise ourselves, we must wean ourselves of our attachment to self-indulgence. It is usually not so difficult to renounce obvious or coarse material gratifications. It is harder to wean ourselves of more subtle attachments, whose negative effect on us might not be so apparent. Therefore, G‑d has promised to complete the process of spiritual circumcision for us. This latter aspect of circumcision will occur in its fullest sense only in the Messianic Era.

Circumcision is the only commandment that is sealed in our physical flesh. Through it, every Jew is connected physically and irrevocably to G‑d, and thus we are given the power to transcend our material drives in order to manifest our true G‑dly natures.1