Jesus had been speaking of his death, but his disciples thought he meant natural sleep.
References for John 11:13
So then he told them plainly, “Lazarus is dead,
and for your sake I am glad I was not there, so that you may believe. But let us go to him.”
Then Thomas (also known as Didymus ) said to the rest of the disciples, “Let us also go, that we may die with him.”
References for John 11:16
On his arrival, Jesus found that Lazarus had already been in the tomb for four days.
References for John 11:17
Now Bethany was less than two miles from Jerusalem,
References for John 11:18
and many Jews had come to Martha and Mary to comfort them in the loss of their brother.
References for John 11:19
When Martha heard that Jesus was coming, she went out to meet him, but Mary stayed at home.
References for John 11:20
“Lord,” Martha said to Jesus, “if you had been here, my brother would not have died.
References for John 11:21
But I know that even now God will give you whatever you ask.”
References for John 11:22
Jesus said to her, “Your brother will rise again.”