Here is Habets commenting on TF Torrance’s view of carnal union and spiritual union with Christ:
Utilizing the language of the Scottish divine John Craig, Torrance distinguishes between Christ’s ‘carnal union’ with humanity from his ‘spiritual union.’ Our carnal union with Christ refers to the union between Christ and humanity through his incarnation. He was made man for us that he might die for us, and so there is a carnal union established between Christ and all of humanity. Our spiritual union with Christ refers to the fact that the Holy Spirit unites the believer with Christ so that the benefits of Christ may be ours. It is important that the carnal union and the spiritual union are not separate but rather, spiritual union is a sharing in the one and only union between God and humanity wrought out in Jesus Christ. (Myk Habets, “The Doctrine of Election in Evangelical Calvinism: T. F. Torrance as a Case Study,” Irish Theological Quarterly 73  338.
This is how Torrance could speak of ‘universal atonement’ (UA) as a necessary corollary of the “Incarnation;” and yet not ‘universal salvation’ (US). UA is the ‘objective’ plank, and in fact the reality and ground by which all of humanity is now oriented to God. The ‘spiritual union’ is the subjective side that is only realized for those who respond to God’s convicting work by the Holy Spirit.
This distinction is different from Westminster Calvinism, which limits Christ’s union with humanity to a certain group of humanity — the elect (thus leaving it open to a charge of Nestorianism). Carnal/Spiritual union allows for a way to speak about election and reprobation in meaningful ways, which are grounded in Christ. In fact, it is this basis which makes this form of Calvinism, Evangelical. All of humanity is represented by Christ, and thus all of humanity is accountable to His ‘salvation’ or His ‘wrath’. Scholastic Calvinism does not place Christ at the center in this way, their basis for God’s wrath, then, is seen outside of Christ — not within. This is a problem, amongst others . . .