What does John 12:29 mean?

The response to Jesus' comment about God's glorification provides insight into how, and why, some people fail to see evidence of God which others find obvious. A voice from heaven speaks audible words (John 12:28). This is the exact communication some modern skeptics claim would compel them to believe in God. However, the core reason for disbelief is not a lack of evidence. Evidence is easily available without miracles (Romans 1:18–20; Psalm 19:1). Evidence is accessible in accounts of the miraculous and in Scripture (John 5:39–40). But evidence can always be dismissed by those who don't want to believe (John 7:17). Miracles can be ignored (Luke 16:31). Signs can be misread, even on purpose.

Those who claim this sound was only thunder seem to be in that latter category. They literally hear the voice of God—and dismiss it as something mindless, natural, and meaningless. That's an appropriate parallel to modern-day skepticism, where mounting evidence of God's influence in nature is brushed aside. Whether it's a lack of spirituality (1 Corinthians 2:14) or outright stubbornness (1 Timothy 4:2), the result is the same.

Others have a less-skeptical interpretation, which is to assume the voice they heard was that of an angel. Both, however, find themselves in a moment of decision. As Jesus will explain, these events serve as "signs" that ought to lead people to faith (John 12:30–36). Those who reject God will have no excuse for their disbelief. Later verses in this same passage make this idea very clear (John 12:37–40).