Illumination is the work of the Holy Spirit by which He opens the minds and hearts of believers to understand, embrace, and apply the Scriptures, enabling them to receive as true and precious the Word they could not rightly grasp by natural reason alone. It must be carefully distinguished from revelation and inspiration. Revelation is God’s disclosure of truth; inspiration is His breathing out of the written Word through the prophets and apostles; both are finished and complete in the closed canon. Illumination is ongoing—not the giving of new truth, but the Spirit’s enabling of the reader to perceive and submit to the truth already given. The natural man, Paul teaches, receiveth not the things of the Spirit of God, for they are foolishness unto him, neither can he know them, because they are spiritually discerned; the things of God are known only by the Spirit of God, whom believers have received. So the psalmist prays, “Open thou mine eyes, that I may behold wondrous things out of thy law,” and Christ opened the understanding of the disciples that they might understand the Scriptures. Illumination does not bypass study, teaching, or the use of the mind; it sanctifies and enables them, removing the blindness of sin and the hardness of heart so that the Word, which is objectively clear, becomes savingly clear to the reader. It is why the same Scripture is foolishness to the perishing and the power of God to the saved, and why prayer for understanding belongs to all right reading of the Word.