Robert Letham’s Union with Christ is a good overview of a subject that is vital for understanding how we receive all the benefits Christ procured through earthly life and death. One of the things I appreciate about his approach is the way he defines “union in Christ” in covenantal categories. Even if appeals to the classical “covenant of grace” / “covenant of works” approach to the biblical covenants, his approach rightly assigns “union in Christ” to a covenantal concept.
Of late, I have heard some people speak about “union in Christ” and Christ’s mediation (a la 1 Timothy 2:5) without paying attention to the biblical idea of the covenants. Letham corrects this sort of approach. He shows how “union in Christ” cannot be explained our understood apart from understanding Christ as a “covenant head” and someone who is united to us in a “covenantal” relationship. Here is how he summarizes his understanding of Union in Christ: