וּנְמַלְתֶּ֕ם אֵ֖ת בְּשַׂ֣ר עָרְלַתְכֶ֑ם וְהָיָה֙ לְא֣וֹת בְּרִ֔ית בֵּינִ֖י וּבֵינֵיכֶֽם׃
And ye shall be circumcised in the flesh of your foreskin; and it shall be a token of a covenant betwixt Me and you.
Read kabbalistic (mystical) interpretation of Genesis 17:11: and classical mystical sources.