The Tanya on the Shema:

On Judaism's most important proclamation, the Shema, Shneur Zalman in the Tanya, Shaar Hayichud VehaEmunah (The Gate To The Understanding of God's Unity and the Faith" Chapter 1, writes:

"Let us understand in a small measure, the statement...that Shema Yisrael...is yichuda ila'ah (higher-level Unity) and Baruch shen kvod malchuto leolam vaed is yichuda tata'ah ('lower-level unity)...

Here, Shneur Zalman is addressing the seeming dichotomy in Jewish thought that God is kadosh kadosh kadosh Adonai t'vaot milo kol aretz kivodo--"Holy is God who fills the whole universe" and the following line from the Kaddish--Baruch kavod Adonai mimkemo, "Blessed is the Lord's glory from his place."

Shneur Zalman is providing the foundation for nondual mystical Judaism in understanding the unity, the ratzo v'shov, the expanding and contracting mind, of our human perception.

In what seems like language that's a bit antiquated, here Shneur Zalman explains that EVERYTHING is God always and constantly:

"if the creative letters were to depart even for an instant, and return to their source all the heavens would be become naught...and so it is with all created things, in all the upper and lower wrolds and even this physical earth and the realm of the completely inanimate...even immobile beings which show no signs of animation harbors within it the Divine life-force."