Watch the sword Nathan promised actually arrive, one household tragedy at a time. David's son Amnon rapes his half-sister Tamar, and David, though angry, does nothing to discipline him (2 Samuel 13:21) — the same failure to confront wrongdoing inside his own house that let his own sin with Bathsheba happen in the first place. Absalom, Tamar's full brother, waits two years and then has Amnon murdered in revenge, flees, and eventually returns to a father who won't fully receive him even after he's brought back (2 Samuel 13–14). What grows out of that half-reconciliation is a son's slow, calculated theft of his father's kingdom — Absalom sitting at the city gate intercepting people with grievances, telling them "there is no man deputed of the king to hear thee," until he's "stolen the hearts of the men of Israel" (2 Samuel 15:2–6) — and finally an open rebellion that drives David out of his own capital, weeping, barefoot, covering his head (2 Samuel 15:30).
David's instruction to his commanders before the final battle — "deal gently for my sake with the young man, even with Absalom" (2 Samuel 18:5) — is one of the most quietly devastating lines in the whole book, because you already know, and David seems to sense, that it won't be honored. Joab kills Absalom against direct orders, and David's response is the rawest grief recorded of any king in Scripture: "O my son Absalom, my son, my son Absalom! would God I had died for thee, O Absalom, my son, my son!" (2 Samuel 18:33). Notice what's actually happening in that repetition — a father who once let a rich man's parable convict him of his own guilt now grieving a son whose entire rebellion grew, at least in part, out of the household he failed to govern honestly after Bathsheba. The sword Nathan named didn't come from outside the family. It came from inside it, generation after generation.