Prior to the modern period the predominant question in the West was, “What has God said?” There were different answers to this question. Rome pointed to the church as the source of revelation and the Protestants pointed to Scripture as read by the church. Both pointed to an extrinsic authority. In the modern period the place of authority moved to within us. We became the measure of all things. Perhaps the greatest question of the modern period (since c. 1650) has been, “Has God said?”
One reaction to the religious doubt and outright skepticism of the modern period has been to do an “end run” around the crisis via direct, unmediated access to the divine mind (rationalism) or to direct, unmediated divine revelation (mysticism) or to immediate experience of the transcendent. The pietist knows that the Christian faith is true because “He walks with me and He talks with me.” In principle, and too often in practice, the pietist simply gives up the historicity of the faith in favor of a subjective encounter with the risen Christ or with the transcendent.
The reaction to the subjective turn is to deny subjectivity in the faith altogether. This denial is a sort of intellectualism. The historic Christian faith is propositional and it is historical and anyone, as they say on public radio, “who says otherwise is itching for a fight.” Nevertheless, is that all there is? Is there any confirmation of the faith beyond what I read on the page in holy Scripture or what I hear in the sermon or eat at the table or see at the baptismal font?
“Beyond” is not the best word. This gets us back to the end-run approach. Better we should say “through.” Reformed folk believe that the Spirit operates through the Word and sacraments. Through the Gospel the Spirit works to make dead sinners alive (Eph. 2). Through faith the Spirit creates existential union with the risen Christ. By virtue of that union, the Spirit creates and fosters communion between the risen Christ and his people.
The psalms are replete with reflection upon the communion between Christ and his people. Consider just one example of Ps. 51:6, “Behold, you delight in truth in the inward being, and you teach me wisdom in the secret heart.” This is a high point in one of the most touching, personal, heartfelt, and intimate prayers in all of Scripture. This is a sinner crying out for the grace of forgiveness and a restored sense of God’s presence.
In Scripture and Christian experience we see seasons where one’s sense of the presence of God waxes and wanes (WCF 18.4). Ps. 21 is evidently the witness of a believer (David, according to the superscription) who is enjoying a rich experience of God’s presence. “For you make him most blessed forever; you make him glad with the joy of your presence.” This presence, which results in joy and peace, is in stark contrast to the presence he describes a few verses later, the presence of judgment and condemnation.
Reformed theology understands that the Spirit operates through the Word by illuminating that Word, by casting light on it, by making clearer what was obscure. Of course, Westminster Confession 1.7 reminds us “all things in Scripture are not alike plain in themselves….” The Spirit does help us to understand what is necessary to know for faith and life. Paul speaks of this illumination when he speaks of “having the eyes of your hearts enlightened, that you may know what is the hope to which he has called you, what are the riches of his glorious inheritance in the saints…. (Eph 1:18)”
The Reformed tradition has written about this aspect of the faith at great length. William Perkins, Richard Sibbes, William Ames, John Owen are just a few of the well-known English writers who have written about these aspects of Christian faith and life. A number of Dutch Reformed writers (e.g. Gijsbertus Voetius and Wilhelmus a Brakel) addressed these same sorts of questions.
What we don’t want to do is to give in either to religious subjectivism or intellectualism. Calvin says in his commentary on Acts 16:14-15,
But we must note the expression that the heart of Lydia was opened so that she paid attention to the external voice of a teacher. For as preaching on its own is nothing else but a dead letter, so, on the other hand, we must beware lest a false imagination, or the semblance of secret illumination, leads us away from the Word upon which faith depends, and on which it rests. For in order to increase the grace of the Spirit, many invent for themselves vague inspirations so that no use is left for the external Word. But the Scripture does not allow such a separation to be made, for it unites the ministry of men with the secret inspiration of the Spirit. If the mind of Lydia had not been opened, the preaching of Paul would have been mere words; yet God inspires her not only with the mere revelations but with reverence for His Word, so that the voice of a man, which otherwise would have vanished into thin air, penetrates a mind that has received the gift of heavenly light.
Therefore let us hear no more of the fanatics who make the excuse of the Spirit to reject external teaching. For we must preserve the balance which Luke established here, that we obtain nothing from the hearing of the Word alone, without the grace of the Spirit, and that the Spirit is conferred on us not that He may produce contempt of the Word, but rather to instill confidence in it in our minds and write it on our hearts.
Tim Challies has a helpful post (from 2004) on this topic here.