To identify a Qur'anic passage's central purpose, first establish its wording and context; then ask which subject category best accounts for its message.
A ruling on worship or trade — legal rulings.
A reasoned answer to a claim of polytheism — argumentation.
Signs in the heavens, earth and provision — divine favors.
The fate of a rebellious earlier community — the days of Allah.
Reckoning on the Day of Judgment — death and the hereafter.
These categories should be used together with attention to evidence, Qur'anic style, reliable early explanation and the limits of human understanding. The combination makes interpretation disciplined and purposeful.