From Anstey’s Doctrinal Definitions:
There are three main ways in which sleep is used in the New Testament:
1) Physical Sleep
This has to do with a person taking his normal rest at night (Matt. 8:24; 13:25; 26:40; Acts 12:6; 20:9, 1 Thess. 5:7, etc.).
2) The Sleep Of Death
This has to do with the spirit and soul of a believer being separated from his body through death (Matt. 9:24; 27:52; John 11:11; Acts 7:60; 13:36; 1 Cor. 11:30; 15:6, 51; 1 Thess. 4:14; 5:10, etc.). This kind of sleep pertains to the believer’s body (Matt. 27:52), not to his spirit and soul which “live unto Him” after death (Luke 20:38). The body is put to sleep in death “through Jesus” (1 Thess. 4:14). That is, He induces death upon His loved ones when He calls them to Himself. This shows us that death for the believer does not happen by accident.
There are at least three reasons why a believer falls asleep in death:
• His work in service for the Lord is finished (Acts 13:36; 2 Tim. 4:6-7; 2 Peter 1:14).
• His death is for the glory of God—i.e. martyrdom (John 11:4; 21:18-19; Phil. 1:20).
• He is taken away from the earth through death by the chastening hand of the Lord (Acts 5:1-11; 1 Cor. 11:30; 1 John 5:16).
3) Spiritual Sleep
This refers to a state of spiritual apathy into which a believer can get through the influence of the world (Mark 13:36; Rom. 13:11; 1 Thess. 5:6; Eph. 5:14, etc.).