John 12:41 records an interesting statement, namely, that Isaiah saw the glory of Jesus. One might wonder how this was possible, for Isaiah lived some seven hundred years before the life and ministry of Christ. But the context helps us understand exactly what John is talking about. John 12:39–40 refers to Isaiah 6:10 and the word given to Isaiah when he was called to ministry and given a grand vision of the holiness of God. Isaiah saw God’s glory (see Isa. 6:1–7), and John tells us that in seeing God’s glory at that point, the prophet saw the glory of Jesus. This is a strong indicator of the deity of Christ, for if Isaiah saw the glory of Jesus when he saw the glory and holiness of the Lord, the prophet must have seen the preincarnate Son of God.
But if Isaiah saw the glory of God when he had his vision of the Lord in His majestic holiness, then we also see our definition of the glory of God fleshed out. That is, when the Bible speaks of the glory of God, it is also making reference to His holiness. And it is doing so in the two main senses of the concept of holiness. First, holiness refers to “set-apartness.” To be holy is to be set apart from what is common, and if God’s inherent glory is something that He will share with no one (42:8), then in His glory our Creator is set apart from all else. Holiness is also used in Scripture with reference to moral purity. So, God’s glory goes hand in hand with God’s purity. The beautiful light of divine glory is so blindingly pure because our Creator is perfectly pure, free of all taint of evil. “God is light, and in him is no darkness at all” (1 John 1:5). Our Creator cannot be tempted with evil, and He tempts no one with evil (James 1:13). God is absolutely pure and free of sin—so pure, in fact, that He is not even capable of sin. This holiness coincides with His glory.
That the light of our Lord’s glory and His perfect holiness go together helps to explain passages such as John 3:19. Taking on human flesh, God became incarnate in the person of Christ Jesus and came into the world as the light of the world. Yet, the result was to confirm wicked men in judgment, for they, being evil, have loved the darkness rather than the light. The darkness of evil cannot stand the light of God’s glory, for it is the light of His holiness. Only when someone’s sin is atoned for can he stand in the presence of divine glory (Isa. 6:1–7). We must be purified in order to endure the glory of God (Heb. 12:14).