Jesus had been speaking of his death, but they thought he meant ordinary sleep.
In context
11He said this, and then he added, “Our friend Lazarus has fallen asleep, but I am going to wake him.” 12The disciples said to him, “Lord, if he has fallen asleep, he will get well.” 13Jesus had been speaking of his death, but they thought he meant ordinary sleep. 14So then Jesus told them plainly, “Lazarus has died, 15and for your sake I am glad I was not there, so that you may believe. But let us go to him.”
