Hizb 42 closes Luqman with a warning against following ancestral custom blindly and one of the Quran's most quoted closing statements, that knowledge of the Hour, of when rain will fall, of what is in the wombs, of what any soul will earn tomorrow, and of where any soul will die belongs to God alone among five things no created being can claim to know.
The hizb then opens Al-Ahzab, the Confederates, named for the coalition of tribes that besieged Medina in an episode known as the Battle of the Trench. It reforms the pre-Islamic practice of adoption, ending the custom of treating an adopted son as a blood son for purposes of inheritance and lineage, a change tied historically to the case of Zayd ibn Harithah, the Prophet's own adopted son. Instructions follow for the Prophet's wives, addressed collectively as Mothers of the Believers, on conduct and modesty befitting their position.
The hizb closes describing the community's fear during the siege itself, hearts reaching to the throats as the sura puts it, and the hypocrites' wavering loyalty exposed under that same pressure, a vivid account of a specific historical crisis rather than a general moral teaching.
The Zaynab marriage and the seal of the prophets verse are often taught together for exactly this reason, since the first resolves a specific social taboo the earlier reform had created and the second states a doctrine of much broader and lasting theological consequence, both landing within the same short stretch of text.