Even as the testimony, etc. Erasmus gives a different rendering, to this effect, "that by these things the testimony of Christ was confirmed in them;" that is, by knowledge and by the word. The words, however, convey another meaning, and if they are not wrested, the meaning is easy -- that God has sealed the truth of his gospel among the Corinthians, for the purpose of confirming it. Now, this might be done in two ways, either by miracles, or by the inward testimony of the Holy Spirit. Chrysostom seems to understand it of miracles, but I take it in a larger sense; and, first of all, it is certain, that the gospel is properly confirmed in our experience by faith, because it is only when we receive it by faith that we "set to our seal that God is true" (John 3:33.) And though I admit that miracles ought to have weight for the confirmation of it, yet we must go higher in search of the origin, namely this, that the Spirit of God is the earnest and seal. Accordingly, I explain these words in this manner -- that the Corinthians excelled in knowledge, inasmuch as God had from the beginning given efficacy to his gospel among them, and that not in one way merely, but had done so both by the internal influence of the Spirit, and by excellence and variety of gifts, by miracles, and by all other helps. He calls the gospel the testimony of Christ, or respecting Christ, because the entire sum of it tends to discover Christ to us, "In whom all the treasures of knowledge are hid" (Colossians 2:3.) If any one prefers to take it in an active sense, on the ground that Christ is the primary author of the gospel, so that the Apostles were nothing but secondary or inferior witnesses, I shall not much oppose it. I feel better satisfied, however, with the former exposition. It is true that a little afterwards (1-Corinthians 2:1) the testimony of God must, beyond all controversy, be taken in an active sense, as a passive signification would not be at all suitable. Here, however, the case is different, and, what is more, that passage strengthens my view, as he immediately subjoins what it is [1] -- to know nothing but Christ. (1-Corinthians 2:2.)

Footnotes

1 - "Quel est ce tesmoignage;" -- "What this testimony is."

Even as - Καθώς Kathōs. The force of this expression seems to be this, "The gospel of Christ was at first established among you by means of the miraculous endowments of the Holy Spirit. Those same endowments are still continued among you, and now furnish evidence of the divine favor, and of the truth of the gospel to you, 'even as' - that is, in the same measure as they did when the gospel was first preached." The power to speak with tongues, etc. 1 Cor. 14 would be a "continued miracle," and would be a demonstration to them then of the truth of Christianity as it was at first.
The testimony of Christ - The gospel. It is here called "the testimony of Christ," because it bore witness to Christ - to his divine nature, his miracles, his Messiahship, his character, his death, etc. The message of the gospel consists in bearing witness to Christ and his work; see 1-Corinthians 15:1-4; 2-Timothy 1:8.
Was confirmed - Was established, or proved. It was proved to be divine, by the miraculous attestations of the Holy Spirit. It was confirmed, or made certain to their souls by the agency of the Holy Spirit, sealing it on their hearts. The word translated "confirmed" ἐβεβαιώθη ebebaiōthē, is used in the sense of establishing, confirming, or demonstrating by miracles, etc.; in Mark 16:20; compare Hebrews 13:9; Philippians 1:7.
In you - ἐν ὑμῖν en humin. Among you as a people, or in your hearts. Perhaps the apostle intends to include both. The gospel had been established among them by the demonstrations of the agency of the Spirit in the gift of tongues, and had at the same time taken deep root in their hearts, and was exerting a practical influence on their lives.

As the testimony of Christ, etc. - The testimony of Christ is the Gospel which the apostle had preached, and which had been confirmed by various gifts of the Holy Spirit, and miracles wrought by the apostle.

(9) Even as the testimony of Christ was (e) confirmed in you:
(9) He shows that the true use of these gifts consists in this, that the mighty power of Christ might be set forth in them, that hereafter it might evidently appear how wickedly they abused them for glory and ambition.
(e) By those excellent gifts of the Holy Spirit.

Even as the testimony of Christ was confirmed in you. By "the testimony of Christ" is meant the Gospel of Christ, which bears a testimony to his deity, his incarnation, his obedience, sufferings, and death, his resurrection from the dead, ascension to heaven, session at God's right hand, and intercession for the saints; to redemption by his blood, justification by his righteousness, pardon and atonement of sin by his sacrifice, and complete salvation by his obedience and death. This, as it had been preached to the Corinthians, was confirmed and established among them, by the signs and miracles with which it was attended; by the extraordinary gifts of the Spirit, particularly of prophecy bestowed on many of them; and by the internal power and energy of the Spirit, accompanying and applying it to their souls.

According as the testimony of (of, and concerning) Christ (who is both the object and author of this testimony [BENGEL]; 1-Corinthians 2:1; 1-Timothy 2:6; 2-Timothy 1:8) was confirmed among [ALFORD] you; that is, by God, through my preaching and through the miracles accompanying it (1-Corinthians 12:3; Mark 16:20; 2-Corinthians 1:21-22; Galatians 3:2, Galatians 3:5; Ephesians 4:7-8; Hebrews 2:4). God confirmed (compare Philippians 1:7; Hebrews 2:3), or gave effect to the Gospel among (or better as English Version, "in") the Corinthians by their accepting it and setting their seal to its truth, through the inward power of His Spirit, and the outward gifts and miracles accompanying it [CALVIN].

The testimony of Christ - The gospel. Was confirmed among you - By these gifts attending it. They knew they had received these by the hand of Paul: and this consideration was highly proper, to revive in them their former reverence and affection for their spiritual father.