To have true knowledge, it is not enough to have God’s clear revelation; a person must also be able to see. And it is exactly at this point that the Holy Spirit enters in, too. He gives a person not only an infallible book but also eyes so that he can read that book.
Some passages show clearly that the opening of one’s spiritual eyes is an act of God and not of a human being. The psalmist, feeling his inability to open his eyes by himself, prays to God to do it when he petitions: “Open my eyes that I may see wonderful things out of your law” (119:18). He has tried to do it himself. He cannot. So he asks God, the only one who can, to open his eyes.
More specifically, however, it is the third Person of the Trinity, and not the Father nor the Son, who illuminates a person’s mind. Just as he is the One who gives natural understanding and wisdom in the first place, so he is also the One who restores this wisdom after humanity has fallen.
This is abundantly clear from Scripture. In 1 Corinthians 2, Paul declares that he did not come to Corinth “with eloquence or superior wisdom” (v. 1) and, he continues, “My message and my preaching were not with wise and persuasive words, but with a demonstration of the Spirit’s power, so that your faith might not rest on men’s wisdom, but on God’s power” (2:4–5).
Later on in this very chapter, Paul reaffirmed the same point by contrasting the natural and the spiritual man (2:14–15). The natural man is blind and therefore cannot receive the things of the Spirit of God. But “the spiritual man makes judgments about all things” (2:15).
In Ephesians 1:18 Paul was also unequivocal as to the fact that it is the Holy Spirit who enlightens the mind. For he prayed, not that the intellect of the believers might be sharpened—nor for new knowledge—but he prayed specifically for the Spirit of wisdom and revelation that “the eyes of their heart” may be enlightened so that they may know the things of the Spirit of God.
The sum of the matter is, then, that when the Holy Spirit comes into people’s lives He enlightens them, gives them understanding, teaches them, opens their eyes, removes the veil from their hearts, and softens their hearts so that they can know the things of the Spirit of God. Without Him, a person is blind to see the truths of revelation; but when there is a demonstration of the Spirit and of power, a person knows all things.