The Levites—standing probably in some convenient spot midway between the two mountains (cf. Joshua 8:33)—were to pronounce with a loud voice the blessing and the curse, so that all might hear; and the people were to give their assent, and take to themselves, as it were, the blessing or the curse as uttered, by a solemn Amen.
By the Levites here are intended, not the sons of Levi generally, but that portion of them which belonged to the priesthood, and bare the ark of the covenant (cf. Joshua 8:33).