John Calvin Commentary John 17:21

"that they may all be one; even as thou, Father, [art] in me, and I in thee, that they also may be in us: that the world may believe that thou didst send me." — John 17:21 (ASV)

That all may be one. He again lays down the goal of our happiness as consisting in unity, and rightly so. For the ruin of the human race is that, having been alienated from God, it is also broken and scattered within itself.

Its restoration, therefore, on the contrary, consists in its being properly united in one body. As Paul declares, the perfection of the Church consists in believers being joined together in one spirit. He also says that apostles, prophets, evangelists, and pastors were given so that they might edify and restore the body of Christ, until it came to the unity of faith.

Therefore, Paul also exhorts believers to grow into Christ, who is the Head, from whom the whole body joined together and connected by every bond of supply, according to the operation in the measure of every part, makes increase of it to edification (Ephesians 4:3, 11-16).

Therefore, whenever Christ speaks about unity, let us remember how basely and shockingly, when separated from Him, the world is scattered. And next, let us learn that the beginning of a blessed life is that we all be governed, and that we all live, by the Spirit of Christ alone.

Again, it should be understood that in every instance in this chapter where Christ declares He is one with the Father, He is not speaking simply of His Divine essence. Rather, He is called one with regard to His mediatorial office and insofar as He is our Head.

Many of the Fathers, no doubt, interpreted these words as meaning, absolutely, that Christ is one with the Father because He is the eternal God. But their dispute with the Arians led them to seize on detached passages and distort them from their natural meaning in order to use them against their antagonists.

Now, Christ’s purpose was widely different from that of raising our minds to a mere speculation about His hidden Divinity. For He reasons from the goal by showing that we ought to be one; otherwise, the unity He has with the Father would be fruitless and ineffectual.

To understand correctly what was intended by saying that Christ and the Father are one, we must take care not to deprive Christ of His office as Mediator. Instead, we must view Him as He is the Head of the Church and unite Him with His members.

In this way, the chain of thought is preserved: to prevent the unity of the Son with the Father from being fruitless and ineffectual, the power of that unity must be diffused throughout the whole body of believers. From this, we also infer that we are one with the Son of God—not because He conveys His substance to us, but because, by the power of His Spirit, He imparts to us His life and all the blessings He has received from the Father.

That the world may believe. Some explain the word world to mean the elect, who at that time were still dispersed. However, since the word world throughout this entire chapter denotes the reprobate, I am more inclined to adopt a different opinion.

Indeed, immediately afterwards, He draws a distinction between all His people and this same world which He now mentions.

The verb, to believe, has been used inaccurately by the Evangelist here for the verb, to know; that is, when unbelievers, convinced by their own experience, perceive the heavenly and Divine glory of Christ.

The consequence is that, believing, they do not believe, because this conviction does not penetrate to the heart's inner feeling. And it is a just vengeance of God that the splendor of Divine glory dazzles the eyes of the reprobate, because they do not deserve to have a clear and pure view of it.

The Evangelist later uses the verb to know in the same sense.