Read Galatians 3:19 Using Other Translations
Wherefore then serveth the law? It was added because of transgressions, till the seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator.
Why then the law? It was added because of transgressions, until the offspring should come to whom the promise had been made, and it was put in place through angels by an intermediary.
Why, then, was the law given? It was given alongside the promise to show people their sins. But the law was designed to last only until the coming of the child who was promised. God gave his law through angels to Moses, who was the mediator between God and the people.