In that culture, crowds of relatives and neighbors commonly showed up at the dwelling of the deceased to mourn. In the midst of this confusion and noise, Jesus declares, "The child is not dead but sleeping." Being ignorant of His use of "sleep" for death, the mourners deride Him.
Christ says the same of His dead friend, Lazarus, in John 11:11. Death as sleep is a euphemism common to many nations. It intimates that, even more sure than morning comes to a sleeper in bed, an everlasting morning will be provided for the righteous dead waiting in the grave for the resurrection. Jesus views death as a temporary sleep because His Father has the power to resurrect anyone from death. God can resurrect whom He wants when He wants, but He has an organized plan, purpose, and schedule for resurrections (I Corinthians 15:20-24; Revelation 20:5-6).
Martin G. Collins
The Miracles of Jesus Christ: Resurrecting Jarius' Daughter