What does John 12:31 mean?

These words come as Jesus is speaking to a group in Jerusalem (John 12:20–22). The main point of His discussion is His impending death—"this hour" and "this purpose" for which He has come (John 12:27). During that conversation, an audible voice from heaven spoke words (John 12:28). Some in the crowd, expressing spiritual stubbornness, dismissed it as noise (John 12:29). Jesus, in contrast, explains the voice was meant for their good, as a means to point them towards the truth (John 12:30).

In the most direct sense, Jesus is still speaking of His upcoming sacrifice on the cross. That moment is the judgment of sin, and the means by which evil will be forever defeated (Hebrews 2:14–15). However, there is a sense in which His words also apply to the idea He just presented: that each person is presented with Christ and must make a decision. Everyone has access to "enough" proof of God (Romans 1:18–20; Psalm 19:1; John 5:39–40). Those who do not believe must choose disbelief (John 7:17; 1 Corinthians 2:14), and take on judgment themselves (John 3:16–18).

This double-meaning is supported by the comments Jesus makes in the very next verse: all men are "drawn to" Christ by the proclamation of His sacrificial death. Not all will actually come, of course (John 6:44). But no one has an excuse for rejecting what God offers, which is forgiveness of sin (John 6:35). After this conversation ends, the gospel of John will emphasize that people are rejecting God in spite of proof, not because there is no proof (John 12:37–40).