Matthew Poole and continuators on Genesis 17:13

13 He that is born in thy house, and he that is bought with thy Money, must needs be Circumcised: And my Covenant shall be in your Flesh, for an Everlasting Covenant .

So it was and is properly in regard of the thing signified to all true Beleivers; and for the sign it is so called because it was to endure through all Generations till the coming of the Messias: The word Olam here and elsewhere rendred everlasting or for ever being oft used to express not only simple eternity, but any long continuance for many ages, yea sometimes for a mans Life. See Exod. 21. 6. Deut. 15. 17. 1 King. 9. 3.