Summary: 1) Nature (1 Thessalonians 5:4–5), 2) Behavior (1 Thessalonians 5:6–8), and 3) Destiny (1 Thessalonians 5:9-11).
You tend to know the maturity level of a person by how they spend their time. If, at the end of the day, you look forward to playing with toys, you're most likely a child. If you look forward to texting or skyping your friends you are most likely a teen. If you look forward to going to sleep, you're most likely an adult. But if it's the clubs, you're most likely a young, single adult. These people of the night like to wear flashy clothing, spend lots of money on alcohol and hang out in loud dance clubs. Generally there are people who live for the day and people who live for the night.
In this passage Paul contrasts night people (unbelievers) with day people (believers). Night people are associated with darkness, sleep, and drunkenness; day people with light, alertness, and soberness. The apostle’s purpose in contrasting the saved and the lost in this passage was to comfort the Thessalonians (4:18; 5:11). Despite Paul’s teaching during his stay in their city (2 Thess. 2:5), they were worried about their future. Exacerbating their fears were false teachers who were attempting to deceive them (2 Thess. 2:1–3). As a result, numerous questions troubled them, questions no doubt relayed to Paul by Timothy, who had recently returned from Thessalonica (3: 2, 6). Paul reassured the troubled new believers in Thessalonica that they would not face God’s wrath. His use of the pronouns “they” and “them” (5:3) distinguishes the Thessalonians from the unbelievers who will experience God’s wrath. He did so by presenting a series of contrasts between night people and day people. Paul gave the Thessalonians a multifaceted description of the distinction between believers and unbelievers, and the implications for each concerning the Day of the Lord. By so doing, the apostle made it plain that the Thessalonians’ fears that they were already in the Day of the Lord were groundless. Believers are light people and will not experience the darkness of the Day of the Lord.
Do you know a person who keeps going from relationship to relationship, scheme to scheme and job to job. Often, they don't look ahead to the consequences of their actions, and eventually just realize that their present situation is not for them. Believers, who have the indwelling Holy Spirit and new natures, through discernment, have the ability to foresee unnecessary problems, and avoid them. Day people deliberately avoid the pitfalls of stumbling in the darkness and want to call others to this enlighten life.
In 1 Thessalonians 5:4-11, we see three distinctive characteristics that set day people (believers) apart from night people (unbelievers). We see their 1) Nature (1 Thessalonians 5:4–5), 2) Behavior (1 Thessalonians 5:6–8), and 3) Destiny (1 Thessalonians 5:9-11).
1) The Distinctiveness of Believers’ Nature (1 Thessalonians 5:4–5)
1 Thessalonians 5:4-5 But you are not in darkness, brothers, for that day to surprise you like a thief. For you are all children of light, children of the day. We are not of the night or of the darkness. (ESV)
The phrase but you introduces a contrast with verse 3, where Paul used the pronouns “they” and “them” to refer to unbelievers who will not escape the Day of the Lord. The familial term brothers/brethren further emphasizes Paul’s point. As God’s children, the Thessalonians would not experience the Day of the Lord, because unlike unbelievers, believers are not in darkness; they possess an entirely different nature. They do not belong to the night; they are not part of Satan’s evil kingdom. They are not in darkness of understanding (that is, spiritual ignorance) or of the moral nature (that is, a state of sin) (Jamieson, R., Fausset, A. R., & Brown, D. (1997). Commentary Critical and Explanatory on the Whole Bible (1 Th 5:4). Oak Harbor, WA: Logos Research Systems, Inc.)
The spiritual darkness/night that engulfs unbelievers includes both intellectual and moral darkness. It is the intellectual darkness of ignorance on the one hand, and the moral darkness of sin on the other; of not knowing what is true, and of not doing what is right. The Day of the Lord is a “day of darkness” (Joel 2:2; Zeph. 1:15); “the day of the Lord … will be darkness and not light …. Will not the day of the Lord be darkness instead of light?” (Amos 5:18, 20). It is for the night people; thus day people need not fear the Day of the Lord; they will not be part of it. God has chosen not to tell his people everything about Christ’s return, but believers know all that they need to know (Barton, B. B., & Osborne, G. R. (1999). 1 & 2 Thessalonians: life application commentary (p. 77). Wheaton, IL: Tyndale House Publishers.).
Please turn to Ephesians 2 (p.976)
All believers once “were formerly darkness, but now … are Light in the Lord” (Eph. 5:8). Earlier in that epistle, Paul graphically described believers’ former lives in darkness: