In his article, From Slaves to Sons, Tim Trumper offers two suggestions which help us better understand Paul’s teaching on the doctrine of adoption. In the first, he makes it clear that both adoption and the new birth are important to understand if we are going to appreciate our salvation. These two truths are not in competition. In the second, he shows how important adoption is to appreciating Paul’s doctrine of salvation by noting how the doctrine of adoption is linked to every part of redemptive history.
“To be clear about Paul’s teaching we need, first, to cease the well-worn (Puritan) practice of confusing Paul’s language of adoption with John’s references to the new birth (notably Jn 1:12-13; 3:1-21; 1 Jn 2:28-3:3).The terms they use construct two distinctive filial or familial models (robust metaphors), which convey differing yet supplementary concepts of our salvation. Whereas John’s model speaks of the birth of the children of God (tekna tou theou) into the kingdom – emphasising their subsequent growth into the image of the Son (huios) – Paul’s refers to the adoption of God’s (mature) sons into his family, and indicates the new status they have in Christ, and all that goes with it: acceptance, assurance, liberty, prayer, obedience and hope (the inheritance).
While the underlying concepts of each model (new life and free life respectively) contribute harmoniously to the one gospel, systematicians of our tradition, following the example of the Puritans, have mistakenly assumed that to express the unity of these concepts requires the conflation of their models. This is not so. We only have the right to mix biblical models when the Scripture itself does so, although to cease the practice will require a (much-needed) fresh approach to the systematisation of the Bible’s theology; what elsewhere I have called ‘biblical dogmatics’.
Clarity in understanding Paul’s adoption model is gained, secondly, by grasping the coherence of his unique fivefold usage of huiothesia (adoption as son). What determines the importance he places on adoption is not the number of times he uses the Greek term, but the manner in which he utilises it. In fact, the five texts may be understood as markers along the line of redemptive history from the first to the last things (protology to eschatology)…Eph. 1:4-5; Rom. 9:4; Gal. 4:4-5; Rom. 8:15-16; 8:22-23.”
Much spiritual profit could be found in tracing the connection between adoption and election, adoption and justification, adoption and regeneration, and adoption and glorification.