In his book, Union with Christ, Bob Letham writes:
Christ has completely identified himself with us. He is one with us. He everlastingly took our nature into personal union. He is at the Father’s right hand in our flesh. In the word of Bishop Christopher Wordsworth’s hymn “See, the Conqueror Mounts in Triumph”:
You have raised our human nature, in the clouds to God’s right hand;
There we sit, in heavenly places, there with you in glory stand;
Jesus reigns, adored by angels, man with God is on the throne;
Mighty Lord, in your ascension we by faith behold our own.
The incarnation is the indispensable basis for union with Christ. Since Christ has united himself to us in the incarnation, we can be united to him by the Holy Spirit.
In itself, the incarnation of the Son of God does not unite us to him, for by itself it does not accomplish salvation. Christ united to himself a human nature, not the nature of the elect–as though the elect had a humanity different from the rest of the human race. Christ’s becoming man was to the end that he make complete and effective atonement for our sins on the cross, defeat death by his resurrection, and ascend in our nature to the right hand of God. There is no incarnation without atonement.
On the other hand, there can be no atonement without incarnation.
[p40-41. It is now two weeks until release. To pre-order Pleased to Dwell in the UK, please click here.]