On Union with Christ (p913-917):
“The intimacy of this language justifies the use of this topic as an ‘existential perspective’ on the work of Christ. For in this aspect of his work he is, in a distinct sense, ‘God with us,’ Immanuel. As in chapters 2–4, we find here the fulfillment of the covenant: ‘I will be your God, and you shall be my people’ (Jer. 7:23). So union with Christ is an exceedingly broad topic. We will see that it underlies all the works of God in our lives: election, calling, regeneration, faith, justification, adoption, sanctification, perseverance, and glorification. All of these blessings are “in Christ.” To study union with Christ is to explore all of these particular blessings, and therefore the vast range of meaning in that little word in.” (p913-914)
In a strongly exegetical, biblical section on Union with Christ (rather than particularly theological) Frame points out both the breadth of the idea of union with Christ in Scripture, as well as the different chronological elements of this idea. In a sense we are united to Christ in the covenant of redemption before time began, united to Christ in His effectual work for the elect before we were born, and united to Christ when we believed in him in our personal history.