Parshat כי תבוא describes the covenant made at הר גריזים and הר עיבל. All of the Jewish were gathered between the two mountains.
Half of the tribes were on Mount Gerizim, and the other half on Mount Eival. The Leviim were at the base of the two mountains. They faced הר גריזים when they recited all of the blessings. They faced הר עיבל when the curses were mentioned. The people answered אמן after each blessing and curse. It must have been quite an impressive scene to have been there and see how all of the Jewish people accepted the word of G-d.
The specific curses that were heard, referred to transgressions done in secret. The public was reminded that Hashem found it particularly offensive to act one way in public and another in private. This was the basis for impressive covenant made at Mount Gerizim and Mount Eival.