Illumination is that doctrine that describes the work of the Holy Spirit in helping the believer to understand God’s Word. Though regeneration is required to rightly understand the Word, while having spiritual eyes comes before having spiritual sight, they are not, strictly speaking, the same event. Rather illumination describes how the Spirit comes to us as believers opening up the Bible.
There are at least two ways we tend to misunderstand this. First, illumination is not the Holy Spirit bringing us new revelation. Our insights into the text are not on par with the text itself. I sought to make this point a few years ago when many charged a well-known radio preacher of failed prophecy when his prediction of the return of Christ failed to come to pass. That preacher did not claim new revelation. Nor did he even claim special, supernatural insight into the text. Rather he argued that his interpretation of the text led him to his conclusion. He was a bad exegete, not a lying prophet.
Second, illumination is not the Holy Spirit giving us a particular text to answer our questions. If, for instance, I am wrestling over a decision to cut all carbs from my diet, and I come upon that text where King David eats the showbread, this is not the Holy Spirit nudging me to eat bread. The Bible speaks of the Urim and Thummim, the breastplate of the High Priest that provided divine revelation from time to time, but the Bible is not our own personal Urim and Thummim.
Instead illumination is when the Holy Spirit helps us understand a given text as it actually is. It is His work as the perfect exegete, helping us poor exegetes try to stay out of trouble. Such is certainly not as glamorous and exciting as the giving of new revelation. It is, however, where the power is. One blessing of a sound understanding of the work of illumination is it helps us have a sound understanding of the importance and work of the Word of God.
Illumination can, indeed should work alongside the Spirit’s work of conviction. Here the Spirit not only helps us understand the text, but helps us understand ourselves. James tells us that the Word of God is like a mirror. It shows us what we are, with all our blots and blemishes. But, James tells us, we are prone to forget. The work of conviction is the Spirit showing us those spots, and helping us not to forget.
In John 14 Jesus promises to send the Spirit, whom He calls “another helper.” A good exegete would ask here, “Helper for what?” The Spirit is the one who beautifies us, who washes the bride, who, in a word, sanctifies us. The work that we need help with is to become what we are being made into, reflections of the glory of Christ. The Spirit, like our Husband, washes us with the water of the Word. Along the way He helps us understand it, to see ourselves in it. He is, however, also the Encourager. He shows us our sin, but reminds us of our standing. We have a long way to go, but we have also already arrived.