Integral to the doctrine of union with Christ is that the person united with Christ shares Christ's new life. This passage (Gal 2:19-21), along with Rom 6, conveys that through union with Christ, a person shares both Christ's death as well as Christ's new life. Because of union with Christ, Paul is able to say that he lives, or that he experiences new life, by faith.
All this goes counter to Calvinism which teaches that a person must first be raised to new life in order to believe. Ignoring the breadth and depth of the newness of life, Calvinists argue that regeneration precedes faith. Nonsense! No one experiences the new life of Christ apart from faith. If you want to be partakers in Christ's resurrection, you must believe. Only through union with Christ do you share Christ's death and resurrection, and only through faith is anyone united with Christ. For God so loved the world that ... whoever believes in him ... has eternal life.
All salvific benefits are wholly located "in Christ" and it is only by faith that we have gained access solely into this grace in which we now stand (Rom 5:2).