Medieval Jewish Philosophy explains that God's Seamless Oneness is the same as His Absolute Infinity. Rabbi Bachya Ibn Pequda proves this with a near mathematical logic.
This morning I realized something interesting. The Bible seems to prefer to call God, "One" ("Echad"), while Kabbalah seems to prefer to call God, "Infinite" (i.e. "Ein Sof"). Since both terms are ultimately the same, I wonder why one Torah topic prefers one description, while the other Torah topic prefers a different one.
It seems to me that one possible answer could be that the Bible is concerned with developing personal relationships between humans and God. Whereas, Kabbalah is concerned with explaining the cosmic relationship between the universe and God.
The Bible was designed for the sophisticate and simpleton alike. It’s interested in telling even the simple person that there’s One Creator Who truly care and is boundlessly open to an emotional, touchy, feely and very personal relationship. For the purposes of promoting this kind of relationship, saying that God is "One" is a great starting point. Something which is “one” is concentrated, gathered in. It’s in a state which the human’s associate with closeness and intimacy - the very foundations of a personal relationship. So thinking of the Creator as a Being Who gathers in and is intimate helps a person feel that He’s truly accessible.
On the other hand, Kabbalah already addresses a more sophisticated audience, one that’s interested in understanding the relationship between the Creator and the universe. In order to get into a discussion like that, a cosmic discussion, the premise must be that the Creator is “Infinite”. Only then, can such a discussion ensue, allowing a mystic or philosopher to get lost in ideas over how finite and Infinite meet. Since the character of Infinity is endlessness, it conveys “distance” - which is a nice foundation for discussing the relative largess of interacting cosmic realms.