Over the next few post I want to take some time to look at the doctrine of illumination. I want to do this partly because the doctrine of illumination is an often overlooked area of theology. A brief look at a few of the more recent systematic theologies will reveal that many times modern day theologians pay little or no attention to the doctrine of illumination. This, however, is not the case in Psalm 119. Psalm 119 is all about the word of God, including how God helps His people understand that word. In this chapter the psalmist not only recognizes the sufficiency of Scripture, but he also recognizes his need for divine enablement in order to understand Scripture. Or, to use the theological term, he understood his need for divine illumination.
The psalmist was not the first person to recognize his need, nor was he the last. B.B. Warfield recognized this need when he said that man needs “a new heart, or in the confession’s language, the inward work of the Holy Spirit, bearing witness by and with the word in our hearts.” To this Calvin adds,
The testimony of the Spirit is more excellent than all reason. For as God alone is a fit witness of himself in his Word, so also the Word will not find acceptance in men’s hearts before it is sealed by the inward testimony of the Spirit. The same Spirit, therefore, who has spoken through the mouths of the prophets must penetrate into our hearts to persuade us that they faithfully proclaimed what had been divinely commanded.
These men, along with the psalmist, understood the importance of the doctrine of illumination. Their emphasis on this doctrine was not philosophical or systematic, but biblical. They emphasized the doctrine of illumination because God’s Word emphasizes the doctrine. For instance, a key passage on the doctrine of illumination is 1 Corinthians 2:10-16:
For to us God revealed them through the Spirit; for the Spirit searches all things, even the depths of God. For who among men knows the thoughts of a man except the spirit of the man which is in him? Even so the thoughts of God no one knows except the Spirit of God. Now we have received, not the spirit of the world, but the Spirit who is from God, so that we may know the things freely given to us by God, which things we also speak, not in words taught by human wisdom, but in those taught by the Spirit, combining spiritual thoughts with spiritual words. But a natural man does not accept the things of the Spirit of God, for they are foolishness to him; and he cannot understand them, because they are spiritually appraised. But he who is spiritual appraises all things, yet he himself is appraised by no one. For who has known the mind of the Lord, that he will instruct Him? But we have the mind of Christ.
This passage contains several important truths concerning the doctrine of illumination. First, illumination is necessary because man is unable to understand spiritual truth on his own. Second, God, specifically the Holy Spirit, is the source of illumination. Third, illumination is only possible for Christians because they are the only ones who have received the Holy Spirit. Fourth, illumination allows believers to “appraise” the things of God, literally allowing them to “have the mind of Christ.” These truths about illumination are clear in this passage, but they are not limited to this passage. Each one of them is supported by the broader witness of Scripture. Thus, the truths of this passage represent a sampling of what the Bible teaches about illumination.
With the biblical data in mind, the doctrine of illumination can be defined in this way: illumination is the work of the Spirit of God empowering the people of God to understand and appropriate the word of God.
 Quoted in Robert L. Reymond, A New Systematic Theology of the Christian Faith, Lectures Delivered at Covenant Theological Seminary, St. Louis, Mo. and Knox Theological Seminary, Fort Lauderdale, Fla. (Nashville: T. Nelson, 1998), 81.
 New American Standard Bible. Nashville, TN: Tomas Nelson Publishers, 1960.