The purpose of the law was to keep a sinful people in the way of salvation until Christ (the descendant) came, inheriting the promises and distributing them to us. Obviously this law was not a firsthand encounter with God. It was arranged by angelic messengers through a middleman, Moses.
But if there is a middleman as there was at Sinai, then the people are not dealing directly with God, are they? But the original promise is the direct blessing of God, received by faith.
If such is the case, is the law, then, an anti-promise, a negation of God's will for us? Not at all. Its purpose was to make obvious to everyone that we are, in ourselves, out of right relationship with God, and therefore to show us the futility of devising some religious system for getting by our own efforts what we can only get by waiting in faith for God to complete his promise. For if any kind of rule-keeping had power to create life in us, we would certainly have gotten it by this time.
Until the time when we were mature enough to respond freely in faith to the living God, we were carefully surrounded and protected by the Mosaic law.
The law was like those Greek tutors, with which you are familiar, who escort children to school and protect them from danger or distraction, making sure the children will really get to the place they set out for.
But now you have arrived at your destination: