What does 1 Thessalonians 5:9 mean?

Paul has used the metaphor of darkness versus light to explain how Christians can live out our knowledge of Christ's upcoming return. Sleeping and drunkenness, which make a person unaware of their surroundings, are associated with nighttime. Christians, in contrast, are "children of light, children of the day" (1 Thessalonians 5:5), and so should be alert and prepared (1 Thessalonians 5:8). The prior verse added the imagery of armor to this spiritual readiness.

Here, Paul explains why this readiness and awareness are so important. This is grounded in understanding that God does not intend wrath to the Thessalonian believers, but has saved them from the wrath he will pour out on earth during the tribulation. Believers will experience complete deliverance from sin, corruption, and mortality at the rapture, when Jesus calls every Christian to be with him (1 Corinthians 15:51–54; Philippians 3:20–21; 1 Thessalonians 4:13–17).

Although Christians are saved now from the penalty of sin and its mastery, at the rapture Christians will be saved completely from the power and presence of sin. All vestiges of sin will be removed from our bodies at that time. As 1 John 3:2 and Philippians 3:20–21 point out, we will be like the Lord when we meet him. In his letter to the Ephesians Paul mentions the sealing of the Holy Spirit as "the guarantee of our inheritance until we acquire possession of it" (Ephesians 1:14). See also Ephesians 4:30.