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Welcome again to Things Unseen. This week on our podcast we've been trying to reflect on things that help us to think in a deeper and more prolonged way about the Lord Jesus. Yesterday we began to reflect on this, that Jesus is one person, the Son of God. And after the incarnation, and wonderfully still now he has two natures, divine and human. And I was hinting that it took serious Christians about four centuries to work out how we can express this in a way that would help us think rightly about Christ on the one hand, and at the same time protect us against muddle headedness or error or even heresy. And the result of these years of hard thinking was a credo statement PR introduced in 451 AD at the Council of Chalcedon, often called the Chalcedonian definition. And I quoted it at length yesterday. I hope you weren't doing anything complicated when you were listening like driving your car, because it was more, I suspect, than any of us could take in. Very theologically Christologically dense. But what I wanted to impress on us by reading it was that it's very carefully worded and it's also very carefully thought through in order to help us think clearly and deeply about Christ. You know, Christians can be a bit impatient with that kind of detailed thinking, can't we? But if we were musicians, we'd not be impatient with those funny squiggles that Beethoven made on pieces of paper. We wouldn't say, oh, it's all just far too complex and dense if, for example, we were listening to the Moonlight Sonata or maybe his sixth Symphony. Nor should we think about these dense words of these great theological statements as too complicated. What they are doing is giving us a beautiful detailed description of our Lord and Savior, Jesus Christ. And if we are impatient, the fault is probably with ourselves. But I want to focus on just one or two details. You see, these theologians weren't just being theoretical. They were concerned about our muddle headedness about ways of thinking about Jesus that keep on recurring but are not really faithful to Scripture. And that's why the definition of Chalcedon is still helpful to us. It can save us from false ways of thinking about Jesus. I want to mention four of them. Two today, the other two tomorrow. As it happens, they're all associated with particular historical individuals, although the views they express were and still are by no means limited to these individuals. Chalcedon says that Christ is perfect in Godhead, co essential with the Father. Is thinking here about Arianism, a view associated with the 4th century cleric called Arius and resisted by the great Athanasius, who was, as you probably know, frequently exiled because of his faithfulness to Scripture and to Christ. Arius and those he influenced held that the Son was the greatest of all God's creation, but not himself. God. Actually, Arius is alive and well in, for example, Jehovah's Witnesses and in many Unitarians. Now, why is this so important? Well, the greatest thinkers in the Christian church have always had a question at the back of their minds when they've thought about our Lord Jesus Christ. It's could this Christ I am describing actually be qualified to be my Savior? If not, then I must be describing him wrongly. So what's the problem with Arianism? Well, it's simple really. If he isn't truly and fully God, he can't really reconcile us to God. Only God can reconcile us to God. If you're alienated from someone else, I can perhaps facilitate a reconciliation, but only that other person can effect the reconciliation. And this is the wonderful truth of the Gospel that Paul expresses in 2 Corinthians, chapter 5, isn't it? In in Christ, God himself was reconciling the world to Himself, not counting our trespasses against us. But then Chalcedon went on to say that the Son is also co essential with us according to the manhood. And here they were thinking about what's called Apollinarianism. Apollinaris lived at the end of the 4th century and was in fact a strong opponent of Arianism. But he emphasized the full deity of the Lord by saying that the divine Logos took the place of the nous, or the rational soul in the incarnation of the Lord. And I think you can see the problem. If Jesus soul, his nous, his mind is not human, but instead replaced by something divine, then the Lord Jesus isn't really co essential with us. He's not actually truly human. And of course, if he's not truly human, he's not really one of us. In fact, he's a kind of superhuman, a superman. And if that's the case, he can't really represent us. He can't be obedient in our place. The fact that he's not truly human actually disqualifies him from being the substitute for our sins and for our salvation. So what Chalcedon is really saying to us is we have a great Savior who was truly one of us, truly like us, sin apart. And that's what qualifies him to be our Savior, and he's God, and that's what qualifies him to reconcile us to God. That's the message of Chalcedon. And I know it may seem hard to think about it, but the more you think about it, the more it will help you to think clearly about the Lord Jesus. And the more you think clearly about the Lord Jesus, the more you'll love him. And we'll talk more about this tomorrow, Sam.
Things Unseen with Sinclair B. Ferguson
Episode: Co-Essential with the Father
Release Date: June 4, 2026
Host: Sinclair B. Ferguson (Ligonier Ministries)
In this episode, Sinclair B. Ferguson reflects on the theological depth behind the identity and nature of Jesus Christ. Building on the previous day’s discussion of the Chalcedonian definition (451 AD), Ferguson explores historical controversies about Christ’s divinity and humanity. He demonstrates how careful theological reflection protects Christian belief and undergirds the confidence believers can have in Christ’s sufficiency as Savior.
“Nor should we think about these dense words of these great theological statements as too complicated. What they are doing is giving us a beautiful detailed description of our Lord and Savior, Jesus Christ. And if we are impatient, the fault is probably with ourselves.”
In "Co-Essential with the Father," Sinclair Ferguson unpacks two major historical errors about Christ's nature—Arianism and Apollinarianism—showing how the Chalcedonian definition safeguards the faith and assures believers of Christ’s full ability to save. His call is clear: deeper understanding of Christ’s nature leads to greater certainty in salvation and deeper love for the Savior. Tune in tomorrow for the continuation of this discussion and the remaining two Christological errors.