Jamieson, Fausset and Brown on Exodus 34:3

3. no man shall come up with thee ... neither ... flocks nor herds--All these enactments were made in order that the law might be a second time renewed with the solemnity and sanctity that marked its first delivery. The whole transaction was ordered so as to impress the people with an awful sense of the holiness of God; and that it was a matter of no trifling moment to have subjected Him, so to speak, to the necessity of re-delivering the law of the ten commandments.