Paul's letter to the Galatians is about three things: (1) it is the apostle's reaffirmation that God has acted in Jesus of Nazareth, whom Paul proclaims as the crucified Christ; and (2) this now means that everything has changed, not in neat supersessionist terms, but rather that Paul's gospel places what preceded it (inter alia circumcision) and all of what comes after our hearing of it in a new light, i.e. that his gospel is the account of why there's a new-but-yet-old basis for salvation reckoned most fundamentally as a new covenant-identity; and (3) that the covenant-identity not just of Israel but henceforth of the entire world will be based on a unitary faith in Jesus as the Christ, and that the Holy Spirit's manifestation will be the proof of that identification. In every way that Paul is the apostle of the Christ crucified, he is in equal measure the apostle of the Holy Spirit.
Paul's letter is about the way in which we are to understand the terms of the identity that comes to us in the Christ who has been "clearly portrayed as crucified." There is no longer any identity per se because in the wake of the Pauline gospel all of the traditional elements of identity have been transformed by God, so that by means of the gospel through identity we will have died to identity. It is thus only when we hear the Galatian letter "with faith" and respond to it in obedience, that is, when we hear it precisely as scripture, that it provides what is our only valid identity in God's eyes: a gospel-based membership in his family that will be the believer's eschatological way forward.