“But ye,brethren, are not in darkness, that that day should overtake you as a thief.”
Paul is now shifting his focus from the unbelieving world to those in Thessalonika who are “brethren,” believers. Those others will be taken unprepared by the day of judgment, but believers should not be surprised. The next few verses describe the contrast between the lives of committed believers when compared to the lives of the unbelieving world. Believers get both a negative and a positive description, because Paul was not naive and was a capable student of human nature. Following the description of believers, Paul exhorts them to be prepared, in accordance with the salvation God has granted for those who trust in Him.
So what is the main characterization of believers? Look at verse 5: “Ye are all the children of light, and the children of the day: we are not of the night, nor of darkness.” In John 8:12, Jesus says: “I am the Light of the world: he that followeth Me shall not walk in darkness, but shall have the light of life.” I John 1:7: “But if we walk in the light, as He is in the light, we have fellowship one with another, and the blood of Jesus Christ His Son cleanseth us from all sin.”
It is very tempting for me right now to go off on a study of all the different ways Jesus is the Light. I’ll have to note that for another time. The most important meaning here is that those who love God and desire to please Him are to walk in the Light: He is the Light. All of our minutes, days, and years are to be lived in the clear light of His love; His Word; His truth; His promised coming to take us to be with Him; the light of His forgiveness, mercy, grace, and truth. When we do so, we will have fellowship with Him, and with others who love Him as we do.
There is no better way to live.