On that very day Avrohom was circumcised with Yishmoel his son. (17:26)
Rav Henoch of Alexander ZY"A said in the name of Rav Bunim of Parshischoh ZY"A, after Rosh Hashonoh there is a hidden Rosh Hashonoh. The first Rosh Hashonoh is revealed one, then there is a hidden one. Parshas Bereishis is Malchius – Crowning Hashem, - as it is the creation of the world. Parshas Noach is Zichronos, as it says "Vayizkor Elokim ess Noach – Hashem remembered Noach. Parshas Vayeiroh is Shofros – referring to The Akeidoh. This all came to a development, when Avrom was called Avrohom, through the Bris Miloh (circumcision).
- Sefer Siach Sarfei Kodesh
If one thinks that we are past Rosh Hashonoh he is mistaken. We must continue the days that we have attained to its greatest extent.