Bede

And he circumcised him on the eighth day, as God had commanded him when he was a hundred years old. Just as Isaac was indeed born during the time of the Old Testament, yet by his very birth he designates the heirs of the New Testament, so the circumcision by which he was consecrated is indeed a sacrament of the Old Testament, but it was foreshadowed in the figure of the grace of the New Testament, by which the world was to be cleansed in Christ from all filth of sin, death, and mortality. …

Commentary on Genesis (Hexaemeron) ↗