What is the ground of the fellowship of the saints? Again and again,1 we must return to the point that it can only be the reconciling Word of God: the Word of the Gospel and the Word become Flesh, the Lord Jesus Christ.
If we read the New Testament closely, and especially Paul’s letters, we begin to see this more and more as the non-negotiable first principle of ecclesiology. It is there in the opening of 1 Corinthians, for example; it is there in the opening of Galatians.
It is also present in the thanksgiving with which Paul begins his letter to the Philippians. In vv. 3-6, he writes:
3 Εὐχαριστῶ τῷ θεῷ μου ἐπὶ πάσῃ τῇ μνείᾳ ὑμῶν 4 πάντοτε ἐν πάσῃ δεήσει μου ὑπὲρ πάντων ὑμῶν, μετὰ χαρᾶς τὴν δέησιν ποιούμενος, 5 ἐπὶ τῇ κοινωνίᾳ ὑμῶν εἰς τὸ εὐαγγέλιον ἀπὸ [b]τῆς πρώτης ἡμέρας ἄχρι τοῦ νῦν, 6 πεποιθὼς αὐτὸ τοῦτο ὅτι ὁ ἐναρξάμενος ἐν ὑμῖν ἔργον ἀγαθὸν ἐπιτελέσει ἄχρι ἡμέρας [c]Χριστοῦ Ἰησοῦ·
3 I thank my God in all my remembrance of you, 4 always in every prayer of mine for you all making my prayer with joy, 5 because of your partnership in the gospel from the first day until now. 6 And I am sure of this, that he who began a good work in you will bring it to completion at the day of Jesus Christ.
I’ve given the ESV translation above, which translates κοινωνίᾳ as “partnership.” This is a possible meaning of the word; Paul would in that case be thanking God that the Philippians have been his fellow-workers.
But that seems to me less likely than “participation” or “fellowship” (cf. συγκοινωνούς μου τῆς χάριτος in v. 7 and the comment of Calvin below). If that is correct, the sentiment of this verse would be similar to what Paul expresses in 1 Cor. 1:9.2
Indeed, we need not choose between these two possibilities–that is, participation in the gospel and fellowship with one another in the gospel–for the latter would follow naturally and of necessity from the former. Here we might attend to John Calvin’s exposition of the verse:
5 For your fellowship. He now, passing over the other clause, states the ground of his joy — that they had come into the fellowship of the gospel, that is, had become partakers of the gospel, which, as is well known, is accomplished by means of faith; for the gospel appears as nothing to us, in respect of any enjoyment of it, until we have received it by faith. At the same time the term fellowship may be viewed as referring to the common society of the saints, as though he had said that they had been associated with all the children of God in the faith of the gospel. When he says, from the first day, he commends their promptitude in having shewn themselves teachable immediately upon the doctrine being set before them. The phrase until now denotes their perseverance. Now we know how rare an excellence it is, to follow God immediately upon his calling us, and also to persevere steadfastly unto the end. For many are slow and backward to obey, while there are still more that fall short through fickleness and inconstancy.
On this reading, fellowship with one another is predicated upon fellowship with God. But it is particularly crucial to mark in what that fellowship consists: it consists εἰς τὸ εὐαγγέλιον, “in the gospel,” the Word of good news about the person and work of Jesus Christ (hence the phrasing in 1 Cor. 1:9, already alluded to above: “the fellowship of [God’s] Son, Jesus Christ our Lord”–it is fellowship “in the gospel” because the gospel tells us about “Jesus Christ our Lord”).
This common gathering around the Word of promise and proclamation is the basis for the fellowship of the saints not just in the beginning, but from first to last. It embraces past, present, and future: ἀρχή, νῦν, τέλος. Thus Paul writes: ἀπὸ [b]τῆς πρώτης ἡμέρας ἄχρι τοῦ νῦν, 6 πεποιθὼς αὐτὸ τοῦτο ὅτι ὁ ἐναρξάμενος ἐν ὑμῖν ἔργον ἀγαθὸν ἐπιτελέσει ἄχρι ἡμέρας [c]Χριστοῦ Ἰησοῦ (“from the first day until now. 6 And I am sure of this, that he who began a good work in you will bring it to completion at the day of Jesus Christ). Until “the day of Jesus Christ,” the Last Day, the assembly of God’s holy people must always be assembly “in the gospel,” as God’s people look to the Word as their summons to life together, their beginning and end, entering into God’s presence only on the basis of what Jesus Christ has done as proclaimed by his messengers.
Paul is insistent on the point throughout his letters, and it cannot be skirted. We must let it do its work; for it is not an ancillary to ecclesiology but its very heart. In other words, the gospel cannot and must not be subsumed under the doctrine of the Church, but rather the doctrine of the Church must be subsumed under the gospel and the doctrine of God. It is only “in the gospel” that there can be any fellowship at all. As we have that fellowship, God continues the work he has begun in us until it is finished. As Paul writes in 1 Cor. 1:9 (again): “God is faithful, by whom you were called into the fellowship of his Son, Jesus Christ our Lord.”