A couple of things recently have been prompting me to write something about what it means for us to be united with Christ. For my part, I think it is one of the key doctrines of the New Testament – I'd say an understanding of union with Christ is essential to an understanding of justification; it's fundamental. It also seems to be a poorly understood doctrine. That's not to say I do fully understand it; I don't, of course I don't. But I think that, by God's grace, I am starting to have a faint idea of some of what it means. So I'll try and write about that. I'm writing for Christians, but others are free to read it.
What Does "Union with Christ" Mean?
The best place to start is probably Romans 6:1-13
What shall we say then? Are we to continue in sin that grace may abound? By no means! How can we who died to sin still live in it? Do you not know that all of us who have been baptised into Christ Jesus were baptised into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life.
For if we have been united with him in a death like his, we shall certainly be united with him in a resurrection like his. We know that our old self was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. For one who has died has been set free from sin. Now if we have died with Christ, we believe that we will also live with him. We know that Christ being raised from the dead will never die again; death no longer has dominion over him. For the death he died he died to sin, once for all, but the life he lives he lives to God. So you also must consider yourselves dead to sin and alive to God in Christ Jesus.
Let not sin therefore reign in your mortal bodies, to make you obey their passions. Do not present your members to sin as instruments for unrighteousness, but present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness.
Romans 6:1-13, ESV
What, according to Paul does it mean for us to be “baptised into Christ” and into his death?
Paul says that our baptism into Christ means that we somehow share in Christ's death – we are crucified with him (v6), we died with him (v5) and are buried with him (v4). Therefore we have been raised in him (v13) and live in him (v11).
Note that Paul doesn't write here that Christ was crucified for us and therefore that we should give our lives for him. Nor does he say that we are compelled not to sin because of what Jesus has done for us, which is what I imagine many of us would say in answer to the question of verse 1. Paul writes that we have been united with Christ in his death and in his resurrection – that because he has died, we have died and because he has been raised, we have been raised, therefore we should be living like it. Christ is not just the pattern for us to follow; he is the template in which we live.
Paul uses the same idea in Colossians 2:20
If with Christ you died to the elemental spirits of the world, why, as if you were still alive in the world, do you submit to regulations...?
Colossians 2:20, ESV
We see the same idea especially in Paul's use of the phrase “in Christ”. I used to think that it was just a throwaway phrase Paul used because it sounded nice, but it isn't; it's fundamental to what Paul is saying and in my opinion is the key to most of Paul's theology.
Paul uses “in Christ” as a way of referring to Christians (e.g. Romans 16:7), but far more often in connection with the blessings we have received. For example:
“the redemption that is in Christ Jesus”
“no condemnation for those who are in Christ Jesus”
“If anyone is in Christ, he is a new creation”
2 Corinthians 5:17
“In him we have redemption through his blood”
“In him we have obtained an inheritance”
“In him you.... were sealed with the promised Holy Spirit”
“God... made us alive together with Christ ... raised us up with him and seated us with him in the heavenly places in Christ Jesus.”
Where do we have to be to receive God's blessings? In Christ. How do we receive God's blessings? In Christ. Where do God's blessings lead? Into Christ.
“speaking the truth in love, we are to grow up in every way into him who is the head, into Christ”
Ephesians 4:15, ESV
Or see 1 Peter 1:8, where the Christians to whom Peter is writing are said to believe into (εις) him.
This brings us back to the idea that our union with Christ is something which is ongoing – it is true in the past, present and future. We have been crucified with Christ (Galatians 2:20), therefore we should be dying to ourselves (Colossians 3:5), and we will one day die in Christ (1 Thessalonians 4:16), unless he returns first. We have been raised with Christ (Ephesians 2:5-6), we are being raised in Christ (2 Corinthians 4:10) and we will be raised in Christ (Romans 8:11).
As Paul says in 2 Corinthians 4:
We are ... always carrying in the body the death of Jesus, so that the life of Jesus may also be manifested in our bodies. For we who live are always being given over to death for Jesus' sake, so that the life of Jesus also may be manifested in our mortal flesh.
2 Corinthians 4:10-11, ESV
This is then wonderful grounds for our assurance. We are in Christ, who lives forever. So when (and if) we finally die, we remain in Christ and so still live. That means that we have a sure and certain hope of the resurrection, because Jesus has been raised and we are in him, as Paul argues in 1 Thessalonians 4:16 “the dead in Christ will rise first.” (cf 1 Corinthians 15:17).
Jesus and Union
But it is not just Paul and Peter. Jesus also speaks about it at length in John 14 and 15, where we see that it is all intertwined with what it means to be indwelt by the Holy Spirit and with the relationship between the members of the Trinity.
“In that day you will know that I am in my Father, and you in me, and I in you.”
John 14:20, ESV
At the start of John 15, we also see that being in Jesus is the key to being able to bear fruit, and that those who do not abide in him are ultimately thrown into the fire and burned (John 15:6).
Colossians 3:3 - "Hidden in Christ"
So, to come back to one of the questions that prompted this, what does Colossians 3:3 mean when it says “For you died, and your life is hidden with Christ in God”?
This whole idea of dying with Jesus and rising with Jesus is a big theme in Colossians 2 (e.g. v12-13). Paul goes on to apply it in 2:20 – that because we have died to the “elemental spirits of this world”, we shouldn't be living worldly lives (in this case submitting to silly rules). Instead (3:1), Paul tells them they have been raised with Christ, and therefore should be setting their mind where Christ is.
That's the context for 3:3, so in context Paul is telling them that their primary identity is in Christ. After all, they have died in him, and have been raised in him. They are only really alive in him. Christ is where they are, so that's where they should be focusing.
The “hidden” refers forwards to v4 - “When Christ who is your life appears, then you also will appear with him in glory.” Their new, risen, in Christ, selves are not obvious. It will only become clear who we really are when Christ appears, and us with him (cf Romans 8:19). For the time being, what is in Christ is hidden.
1 Corinthians 6 and Sex
Another application of this is in 1 Corinthians 6, where Paul links the idea of our union with Christ with the idea that sex is an expression of and brings about union between man and woman. Paul therefore argues that for someone who is united with Christ to be united with a prostitute is crazy. Of course, the linking of union with Christ and union in sex both point forwards to the perfect consummation of the union between Christ and his bride the Church that awaits us in heaven.
Union with Christ is the means of our salvation – God counts us as righteous because and only because we are in Christ. We are raised from the dead both spiritually and physically only because Christ has been raised from the dead and we are united with him.
Union with Christ is the goal of our salvation. We are growing up corporately into him, and one day we will be perfectly united with him. This means our current union with Christ gives us a sure and certain hope for the future, because we know that what happens to Christ will also happen to us, just as what happened to Christ in his incarnation, rejection, suffering, crucifixion, resurrection and glorification is also happening to us.
Union with Christ gives us our identity - if we are in Christ, we are who we are in Christ, and nothing else.