The Christian’s “union with Christ” is the mysterious dark matter of the spiritual cosmos, so to speak. It is a kind of glue that holds us together with the constellation of salvation and sanctification and glorification in Christ.

And it is very hard to describe and explain.

How, then, can we talk about it? Is such a mystery too deep for words? Where do we begin — and where should we stop? And in our search to explain this new bond to Christ, can we use the language of mysticism? How much of our union with Christ is legal and positional, and how much of it is felt?

With these important questions brewing, I called Sinclair Ferguson, author of the new book Devoted to God: Blueprints for Sanctification. He has been talking about union with Christ for a long time and is as good a teacher as any on this vital subject.

1: Is union with Christ objective or subjective?

Sinclair, how much of our union with Christ is forensic (legal, positional, objective), and how much of it is biological (subjective, felt, affectual)? How do we think about these two seeming polarities?

In Paul’s theology, the believer has one single union with Christ (and Christ with the believer), and this union is multi-dimensional. So rather than just having two halves that we are trying to put together and balance together, we just think of the reality of the union in the same way.

This is one reason why the marriage analogy in Scripture is so helpful. We don’t have two marriages with our spouse — one legal and one spiritual, or one legal and one biological. People may go through a civil ceremony and a Christian ceremony, but in the end it’s just one marriage, a single relationship. In the case of our union with Christ, it’s a single relationship with multiple dimensions.

The concept of one union with many dimensions is helpful. Of all people, Rudolf Bultmann (1884–1976) said that the preposition into (εἰς in Greek) — into Christ — has no parallel to be found in classical Greek for that kind of language, in terms of the relationship between two people (Romans 6:3; Galatians 3:27). The relationship attaches to the whole question of the mystery of this reality. What Paul sees in the gospel is such a multi-dimensional singularity that it creates a new style of language, without parallel.

Of all people, Bultmann lifted my soul to the heavens and caused me to think: What a glorious thing it is to be united to Christ! It was one of those unexpected moments in life.

This is why the marriage analogy is so useful. In Paul’s mind there is no tension between the constitutional or forensic or federal or legal or declarative (or whatever you want to call it) and the existential reality. Just as in marriage, the vow and the covenant and the legal bond all belong together with the affectional dimensions of marriage.

2: Is it appropriate to use mystical language for our union with Christ?

Keeping those things together is glorious. As you know, John Murray wrote an incredible chapter on union with Christ at the end of his 1955 book Redemption Accomplished and Applied. He says, “Here indeed is mysticism on the highest plane. It is not the mysticism of vague unintelligible feeling or rapture. It is the mysticism of communion with the one true and living God” (183). Reformed theologians typically don’t touch the mystical language. Any mention of mysticism gets a raised eyebrow, and for good reasons. But what are the healthy confines of mystic language when describing union with Christ?

Well, first, knowing professor Murray’s understanding, I kind of wish he had put the chapter on union with Christ at the beginning of the second half (“Redemption Applied”) rather than at the end, because he makes clear that our union with Christ is not just another element in the application of redemption. Union is the reality that holds the redemption and the application together. Maybe he left it to the end like keeping the good wine to the last?

But in talking about “mysticism on the highest plane,” it makes me wonder if I use the language frequently enough to satisfy professor Murray.

On a purely personal level, it was professor Murray who really set me in the right direction when I was a teenager wrestling with union with Christ. I was reading things that I couldn’t make head nor tail of, until I read his commentary on Romans and Redemption Accomplished and Applied.

What I think that professor Murray is saying is that this is not the mysticism of vague, unintelligible feeling. He is saying that there are certain negatives here that we should have plainly in our minds when we speak about the mystical union with Christ.

Three warnings will help us not lose our way.

First, in speaking of mystical union, we must never emphasize the emptying of the mind rather than the filling of the mind with Scripture. In John 15:1–11, we see the blessedness of our union with Christ in and through the word of Christ. The more the word of Christ dwells in us richly, the more fully the joy of Christ dwells in us.

Second, in speaking of mystical union, we must never go beyond the revelation of God in Scripture to the notion of discovering God as he is in himself. In more than one place, Calvin says it is only fools who try to do that, to get beyond the attributes of God to find the being of God.

Third, in speaking of mystical union, we must not lose our Trinitarian mooring. Mysticism-gone-bad leads to mere monotheism rather than Trinitarianism, and often it leads to either panentheism or straightforward pantheism. Also, I think that in some of the mystics, you do get a loss of the God/man distinction — so that we lose our identity in God. And I think that the God/man distinction is of utmost importance to our understanding of creation and also to our understanding of redemption. Once we cross that line, we are in trouble.

These three things would be beyond the circumference, I think, for professor Murray’s use of the mystical language.

But again, the marriage analogy is helpful here. This is the difference between the ability to describe your own marriage relationship and actually having that marriage relationship. It’s not the same thing. In marriage, there is always something mysterious, something indefinable about the nature of the relationship. And I think that sometimes we may be nervous about this kind of language because we feel the loss of control. But I think that there is a healthy use, as professor Murray says, “This is mysticism on the highest plane.” And I think that one could add that this is mysticism on a biblical plane, too.

3: What remains a mystery to you about union with Christ?

Speaking of the mystery of our union with Christ, in all its multiple dimensions, after all these years of diving into the ocean of God’s revelation, and coming up with answers to some of those questions, what do you not understand about union with Christ? How much remains a mystery to you?

I’ll return once again to the marriage analogy. I have known my wife from about the time I began to get clear on union with Christ — 45 years ago. That means, I have known her for about 16,000 days. I know so much about her, and I could go on and on about what is so admirable about her. How amazing I think it is that we ever got married in the first place! I felt I was from the wrong side of town, and from the wrong kind of house, and how I married upwards, and I remember all that she has done for me, for my family, for my life, in these 45 years.

I say this partly humorously, but also truly: after 45 years of discovery, I still don’t fully understand her. And I think that is the point. To go back to professor Murray, somewhere in connection with our doctrine of Scripture — and I think that this is true of all areas of theology where we are talking about the divine-human engagement — we come to a point where we have reached the circumference of biblical revelation. And I think that what we are called to do, as professor Murray says of the context of Scripture, is just to look and wonder and awe and praise and realize: There is a world beyond what we can presently understand, and we will know more when we see him face to face.

But in a sense, there will always remain this great affection, in our union with Christ, that we can never fully grasp. For the sake of this union, Christ remained in the bosom of the Father, but brought the bosom of the Father to us. Christ was incarnate, humiliated, and obedient unto the death of the cross. There is an element of it in the seraphim’s cry, “Holy, holy, holy” (Isaiah 6:3). And each time they cry “holy,” it is not mere repetition, but you get the sense that they mean it even more than they did the last time. They catch a fresh glimpse of what “holy” means.

You know, we might go around the circumference of all the texts on our union with Christ, and then enter more and more into the bliss of it. We recognize that we are always admiring it, and we are never at the position of saying, “We’ve got it now. We’ve mastered it now.” No. Union is not something we master. We are forever diving deeper into the meaning of our union to Christ.

In the end, union with Christ is fellowship with the One who has mastered us, and I think that is what makes it so limitlessly wonderful for us, both now and forevermore.