Adam Clarke's Commentary on the Bible

Verse 4 (John 11:4)

This sickness is not unto death - Not to final privation of life at this time; but a temporary death shall be now permitted, that the glory of God may appear in the miracle of his resurrection. It is very likely that this verse contains the message which Christ sent back, by the person whom the afflicted sisters had sent to him; and this, no doubt, served much to strengthen their confidence, though their faith must have been greatly exercised by the death of their brother: for when this took place, though they buried him, yet they believed, even then, probably on the ground of this message, that Jesus might raise him from the dead. See John 11:22 .

- Adam Clarke's Commentary on the Bible