(1) Who the Person is (all three are God, but no Person is the other Person);
(2) What the Person does (the Father sends the Son; the Son secures salvation; the Holy Spirit seals salvation; etc.)
While this dichotomy is actually helpful in laying a foundation, it doesn’t always do justice to the intricate ways in which the Persons work together in the economy of salvation. In The Word Enfleshed: Exploring the Person and Work of Christ, Oliver Crisp offers an example of doing it well, discussing how the Holy Spirit works in our union with Christ:
“It is as if the Spirit acts as a kind of adhesive, preparing and enabling the human subject to be joined to the body of Christ. Like the glue that holds together a composite object that is made up of different parts, such as a piece of furniture or some other artifact, so the Spirit “glues” us to Christ. We become part of his body really and truly—as really and truly as the foam, wood, tacks, fabric, and glue form the one composite object that is an armchair. …
His work is personal, intimate, the real union of one organism to another, the bringing about of a whole new body that is the body of Christ. We might say that just as the Holy Spirit generates and prepares Christ’s human body at the incarnation, so he generates and prepares Christ’s bride, his ecclesiastical body, which in one sense will be complete at the inauguration of the eschaton, when God’s ultimate end in creation will be accomplished and creaturely participation in the divine life begins in earnest.” (161)
So it’s not simply that we’re united with Christ by grace through faith—we’re united to him, held together with him, and made more like him by the indwelling of the Spirit. Of course, we know that the Spirit was intricately involved in both the incarnation and resurrection of Christ, but we also know he is often overlooked or undervalued in the economy of salvation. Crisp points out here one of the many, many ways in which the Spirit works alongside the Father and Son in salvation.
The Persons always work in unison, and no piece of salvation happens without the involvement of each Person. This is why we can say with Fred Sanders that “the gospel is Trinitarian, and the Trinity is the gospel.” May we continue to plumb the depths of the ways in which the unity of the Trinity transforms our hearts and all of creation.