The Spirit uses the word of God alone to speak to his people.

"How diabolical, then, is that madness which pretends that the use of the Scripture is only transient and temporary, which guides the sons of God to the highest point of perfection! I would also ask them another question - whether they have imbibed a different spirit from that which the Lord promised to his disciples? Great as their infatuation is, I do not think them fanatical enough to hazard such an avowal. But what kind of Spirit did he promise? One, truly, who should 'not speak of himself,' but suggest and instil into their minds those things which he had orally delivered. The office of the Spirit, then, which is promised to us, is not to feign new and unheard of revelations, or to coin a new system of doctrine, which would seduce us from the received doctrine of the Gospel, but to seal to our minds the same doctrine which the Gospel delivers." - John Calvin, The Institutes, I. IX. I.

"But in the same place the Apostle also calls his preaching 'the ministration of the Spirit;' doubtless intending, that the Holy Spirit so adheres to his own truth, which he hath expressed in the Scriptures, that he only displaces and exerts his power where the word is received with due reverence and honour. Nor is this repugnant to what I before asserted, that the word itself has not much certainty with us, unless when confirmed by the testimony of the Spirit. For the Lord hath established a kind of mutual connection between the certainty of his word and of his Spirit; so that our minds are filled with a solid reverence for the word, when by the light of the Spirit we are enabled therein to behold the Divine countenance; and on the other hand, without the least fear of mistake, we gladly receive the Spirit, when we recognize him in his image, that is, in the word. This is the true state of the case." - Ibid. I. IX. III.

There is no separating the agency of the Holy Spirit from the knowledge of the truth. To know the truth is life eternal; and this life is begun and supported by the Spirit of Christ. On the other hand, all who resist the truth, and do not admit its evidence, are expressly said to resist the Holy Ghost. We ought not, then, to imagine, with the popular preachers that the gospel can in any respect be considered as a dead letter, or destitute of Divine power. For being the voice of God, it is unchangeably powerful to save all who believe it, and to destroy all who oppose it. Believers are said to grieve the Holy Spirit, when they neglect to hearken to the words of the gospel, and their consciences are answerably grieved, when they are brought to repentance. - Robert Sandeman, Letters on Theron and Aspasio