In case we missed it yesterday, today's first reading repeats Paul's exhortation, "For freedom Christ set us free; so stand firm and do not submit again to the yoke of slavery." The reading practically serves as a vocabulary list of some of Paul's key words: freedom, law, grace, faith, righteousness, LOVE.
Paul was writing to the Galatians, a community in the hinterlands that had received the Gospel from an ailing Paul, nursed him back to health and sent him on his evangelizing way. And then, hearing about the Mosaic covenant and the kosher laws, they became enamored of these, even going so far as to accept circumcision in order to be sure they covered all the bases of salvation. This is what Paul objects to so strenuously. Jesus makes the same complaint in today's Gospel: they are focusing on the wrong thing!
What should have helped them acquire a sacramental worldview, in which "the world is charged with the grandeur of God" (in Hopkins' words). Holiness is not a matter of observing precepts, but of responding to the grandeur of God.
That is why Paul warns the Galatians about the yoke of slavery: they are at risk of submitting to a pattern of rules, rather than keeping themselves open to responsive surrender. In the first case, an objective expectation to fulfill; in the second, an open-ended availability to maintain. In the first case, the rule is central (and "he who does these things shall live by them"); in the second, it is the person (of God and of neighbor) who is kept before one's eyes so that "faith works through love." Paul is pointing to an ever-present danger for religious types (and even for the Church itself): to objectify the response to God, to codify it in a way that sets us free from the commitment to open responsiveness, and offers the more satisfying possibility of a measuring-rod to hold oneself (and others!) to.
As Paul will say elsewhere, there is a law, all right, but it is the law of Christ, the law of self-giving love that Paul actually models for his communities.