Until now we’ve assumed that an 8th day circumcision overrides the restrictions of Shabbos, but how do we know that? It’s not written explicitly in the Torah. All the Sages agree on this law, but they dig hard to find its exegetical basis and never really get there. At the end of the day, it appears that the law was given to Moses at Sinai and/or implied by God when he detailed communicated it to Abraham along with 13 mentions of the covenant between God and Abraham’s descendants. Spiritually speaking, the 8th day represents beyond seven: beyond the seven days of creation, and thus connects to infinity.