But two who sit and exchange words of Torah, the Divine Presence rests amongst them, as is stated, "Then the G-d-fearing conversed with one another, and G-d listened and heard; and it was inscribed before Him in a book of remembrance for those who fear G-d and give thought to His name" (Malachi 3:16).
In the first part of the mishna, two indviduals were united by silence and mutual rejection. In this part, they are united through conversation. But they are not only united, the Divine Presence rests among them.
How does this work? How does two become three?
Shekhina, Divine Pesence, is a mysterious concept. We do know that it is called in Kabbalistic sources, Knesses Yisroel - the gathering of Israel. A clue is that the very term Sheckhina come for the verse in Exodus 25:8, "They shal make me a sanctuary and I will dwell(shakhanti) amongst them".
There are various levels of Shekhina, from the very highest to the ones that we sense among us, all really one and the same(See the beginning of Maamar Bosi L'Gani). The godliness that exists among us is inseparable from the basic defining quality of humans, that we know each other as humans only through and in terms of human society and relationship. To restate it in simple but perhaps shocking terms so to say that G-d only exists in the human realm of relationship and community. If there were not a society of inter-related human beings to sense and enshrine G-d as the King and Master, Friend and Parent, Helper and Judge, there would, perhaps be no Hashem in this world, except as distant Cause.
If a tree falls in the forest and no one hears it, does it really fall? Had there been no humans, would there be G-d (at least in the terms that we understand and perceive him)?
This is what He wanted. "G-d desired to have a dwelling place in the lower worlds (Dira B'Tachtonim( Tanchuma Pikudei2)".
When two individuals share disdain and rejection, they are united by negatvity. But, Hashem is not there, for that is not an interaction that humans can share with the Master of the World, because any rejection between Hashem and humans is one sided. Hashem never rejects. When two people sit and positively interact, especially when they speak of Torah (within which Hashem is enclothed through a different and distinct mechanism), Shekhina dwells among them, for godliness is an aspect of every human interaction. We are only human in as much as we relate to G-d.