Moses called to Aaron and to his sons and to the elders of Israel. And he said to Aaron, "to the Israelites you shall speak, saying, 'Take…offerings to sacrifice before the LORD."Why did Moses not instruct the people directly? From this point onward Aaron was to be the High Priest and in charge of the sacrifices. To demonstrate Aaron's new authority, explains the Ramban, Moses gathered the elders to witness the beginning of Aaron's new position. This way they would see that Aaron was not usurping power for himself but rather, he was humbly following the exact instructions of Moses.