Two is where a tradition has to decide whether difference is a fault or the condition of anything happening at all, and traditions divide sharply on the answer.
Chinese thought takes the second view without hesitation. Yin and yang are not opposed forces to be resolved but paired aspects whose alternation is what the world consists of, and the Book of Changes encodes them in the broken and unbroken line from which every one of its sixty-four figures is built. Neither term is the good one. A world of pure yang would be as broken as a world of pure yin.
Iranian religion takes the first view and makes it the centre of everything. Zoroastrian teaching sets the beneficent spirit against the destructive one as a genuine conflict with a genuine end, and that framing passes into later dualist movements that treat matter itself as the wrong half of the pair. Gnostic and Manichaean systems inherit the structure and radicalise it.
Jewish and Christian scripture uses two more often as a structure for choice than as a metaphysics. The two tablets of the law, the two ways set before the people in Deuteronomy and reused in early Christian instruction, the two pillars Boaz and Jachin standing at the porch of the temple: these mark a decision or a threshold rather than a war.
The Greek arithmologists came down on the pessimistic side. The dyad is the first departure from unity, the principle of division and of the unlimited, and in the table of opposites it stands with everything the tradition mistrusts.