To fit the doctrine of our union with Christ into the order of salvation presents a bit of a challenge, to say the least. Phrases such as in Christ, in Him, in the Beloved, Christ in you - all pointing to union - take on different textures of meaning when considered in the context of passages in which they're located. It's in that light that I find helpful the following section from John Calvin's commentary on John. He interrelates concepts such as God's fatherly love for the elect before creation, God's love in Christ for us while yet enemies, God's effectual call, the faith which embraces Christ, and our union with God through Christ. As I understand it, these are various threads of God's identification with his people - those he chose in the Beloved and redeemed in Christ - all pointing to different shades of God's union with his people.
These words remind us that the only bond of our union with God is, to be united to Christ; and we are united to him by a faith which is not feigned, but which [union] springs from sincere affection, which he describes by the name of love; for no man believes purely in Christ who does not cordially embrace him, and, therefore, by this word he has well expressed the power and nature of faith. But if it is only when we have loved Christ that God begins to love us, it follows that the commencement of salvation is from ourselves, because we have anticipated the grace of God. Numerous passages of Scripture, on the other hand, are opposed to this statement. The promise of God is, I will cause them to love me; and John says, Not that we first loved Him,  (1 John 4:10.) It would be superfluous to collect many passages; for nothing is more certain than this doctrine, that the Lord calleth those things which are not, (Romans 4:17) raises the dead, (Luke 7:22,) unites himself to those who were strangers to him, (Ephesians 2:12,) makes hearts of flesh out of hearts of stone, (Ezekiel 36:26,) manifests himself to those who do not seek him, (Isaiah 65:1; Romans 10:20.) I reply, God loves men in a secret way, before they are called, if they are among the elect; for he loves his own before they are created; but, as they are not yet reconciled, they are justly accounted enemies of God, as Paul speaks,
- When we were enemies, we were reconciled to God by the death of his Son, (Romans 5:10.)
On this ground it is said that we are loved by God, when we love Christ; because we have the pledge of the fatherly love of Him from whom we formerly recoiled as our offended Judge.