Sefiras HaOmer and its place at the end of the Siddur (by the Alter Rebbe himself). Page 114-15.

The question: why did the alter Rebbe place Sefiras HaOmer at the end, when no one else does. It is because he holds that it reveals the very essence of what the Siddur is both on Halachic and Kabbalisitic grounds. Page 115-16.

Beginning of the answer. Davening has a Halachic and Kabbalistic dimension and both are represented well by Sefiras haOmer and he therefore puts it at the end of the siddur. Page 116.

The third point is that if one influences only himself that is good enough, but he has the power to affect the world also, like by Sefiras HaOmer, that counts days and (also) gets us to Shavuos. The Alter Rebbe follows but does not imitate the Arizal, as the Arizal wrote his Siddur for actual…

Explanation of previous class. Sefira is first about us and second about Hashem. Two levels of sacrifice to Hashem.