Our ancestors were commanded that after crossing the Jordan River and entering their promised land they would gather at the site of Mount Gerizim and Mount Eival. Six tribes ascended one mountain and six the other while in the valley between them stood the Kohanim, Levites and the Holy Ark.
The Levites would first face Mount Gerizim and announce the blessing that would be bestowed upon those who refrained from committing a certain sin. All twelve tribes would offer a chorus of "Amen". Then the Levites would turn to Mount Eival and declare the curse that would be visited upon one who committed that sin. Once again all joined in the saying of "Amen".
This procedure was repeated for a dozen different sins. The one message that came forth from these two mountains was that it was up to every Jew to choose between bringing a blessing or curse upon himself.
