The formation of Christ in the believer is not to be reduced to a sharing, on the part of the believer, in the faith of Christ and the concomitant abandonment of relying on works of the law. The Christian, in Paul’s view, does not reject the works of the Torah simply to rely on “faith alone” (whether Christ’s or his or her own). Rather, the Christian relies on that which faith has allowed him or her to receive—the Holy Spirit, which is truly that which stands in contrast with Torah in Galatians, and not “faith.” “Faith in Jesus Christ” is an abbreviated expression for “relying on that which trusting Jesus has brought to the one who trusts,” namely, the actual benefits of Christ’s passion, death, and resurrection. In Galatians, the most fully foregrounded of these benefits is the Holy Spirit, that divine, indwelling gift who empowers the recipient for, and guides the recipient into, a life of righteousness, that is, conformity with the righteous demands of the God who will judge the living and the dead. Paul expresses this end result more eloquently as “Christ living in me” (Gal 2:20) or “Christ [being] fully formed in you” (Gal 4:19).
David A. deSilva, The Letter to the Galatians, ed. Ned B. Stonehouse et al., The New International Commentary on the New Testament (Grand Rapids, MI: William B. Eerdmans Publishing Company, 2018), 386–387.