John Calvin Commentary Joshua 8:33

"And all Israel, and their elders and officers, and their judges, stood on this side of the ark and on that side before the priests the Levites, that bare the ark of the covenant of Jehovah, as well the sojourner as the homeborn; half of them in front of mount Gerizim, and half of them in front of mount Ebal; as Moses the servant of Jehovah had commanded at the first, that they should bless the people of Israel." — Joshua 8:33 (ASV)

And all Israel, and their elders, etc. The third instance of obedience was placing all the tribes on Mount Gerizim and Mount Ebal to stand in six rows each, opposite each other. For they were so arranged that six stood on Mount Ebal, and an equal number on the opposite Mount Gerizim.

The intervening space was occupied by the Levites with the ark of the covenant, so that the Lord would be surrounded on all sides by His own people. It is said that Joshua stood so that he might first bless the people, as it was the purpose of God to attract the people to Himself by kindness and gracious condescension.

For although Moses, to rebuke the obstinacy of the people, mentions only curses, it is certain that these were in a way incidental, because the primary method was to use blessings as a means of winning to obedience those who might otherwise have been rebellious. But when this kind invitation proved ineffective, curses were added as a new resource and remedy.

God had promised ample rewards to His servants who would obey the Law. On the other hand, curses were denounced to deter transgressors. Each is now compelled to affirm his own condemnation, while an "Amen" is responded to every single sentence. For in this way they not only hear themselves condemned by the mouth of God but, as if they were heralds sent by Him, they also pronounce the punishment that may await them.

A similar promulgation was made in the plain of Moab beyond the Jordan, but now they are bound more solemnly and acknowledge the condition on which they are to dwell in the land of Canaan. That the children also were admitted as witnesses added considerable weight to the whole.