What does John 11:13 mean?
Jesus often spoke of spiritual ideas using metaphors which were taken too literally. This is seen in His comments about the destruction of the temple (John 2:19–22), about spiritual rebirth (John 3:4), living water (John 4:11), and spiritual freedom (John 8:31–33). Sleep is a common Christian metaphor for death, when applied to those who die with faith in God (Acts 7:60; 1 Thessalonians 4:13–18).The disciples assumed Lazarus was merely sleeping to recover from illness (John 11:1–3). After all, Jesus sent back an encouraging reply to the messenger (John 11:4), then waited two days to decide to visit Lazarus (John 11:6–7). They're not keen on returning to Judea, since the local religious leaders want to kill Jesus (John 5:18; 11:8). When Jesus seemingly reiterates the idea that Lazarus is "sleeping," they're baffled as to why it's necessary to go there to wake him up.
What they don't understand, Jesus will partially explain in His reply, shown in the next verse.