Dunn delineates three main aspects of the beginning of salvation:
1) justification by faith
2) participation in Christ
3) the gift of the Spirit
Each corresponds to a member of the Trinity: right with God the Father, united to Christ the Son, indwelt by the Spirit.
I find that helpful. This is pp. 334-441 of The Theology of Paul the Apostle.
Here's a good quote from the participation in Christ section:
Paul's motivation, both in his conversion and missionary work, was not the inspiration of a heroic tale of what Jesus taught or did two decades earlier. He was not involved in a Society to Celebrate the Memory of Jesus of Nazareth. Rather, his conception of Christ was of an open channel between God and his people, a living intermediary through whom God acted and through whom his people could approach him. (406)