Matthew Poole and continuators on Genesis 17:11

11 And ye shall circumcise the flesh of your fore-skin ; and it shall be a token of the covenant betwixt me and you.

(i. e.) By an usual Hypallage, the fore-skin of your flesh: And the word Flesh is here put for the Genital part, as it is Levit. 15. 2, 19. Ezek, 16. 26. and 23, 20. and elsewhere. This part God singled out for this Ordinance, because it is and was a great instrument both in the commission of actual sins and in the propagation of original sin, and therefore it was very proper to apply to it the seal of Gods gracious Covenant for the remission of sins past, and the extirpation of sin for the future.

(i. e.) A sign, evidence and assurance, both of the blessing promised by that God who appointed this Ordinance, and of mans obligation to the duties required, which is signifyed by his acceptance of and submission to this Ordinance. And here we have the nature and definition of a Sacrament, viz. that it is a figure or token of Gods Covenant.

Marginal references: Act. 7. 8. Rom. 4. 11.