English: Four, and four, and four — that is eight… It turns out that there are forty-eight covenants for every single commandment.
On the daf: The particular arur statements (including the prohibition of relations with a sister) are read within a larger framework that multiplies covenantal force: each commandment was accepted under multiple sets of oaths (Sinai, Arvos Moav, Gerizim/Eival, etc.), yielding forty-eight berisos for every mitzvah.
Type of Learning
Custom (structural / aggadic unification of the arur series).
What Is Learned
The prohibition is reinforced within the covenantal framework that treats the whole series of curses as a comprehensive national commitment covering every commandment.