I Thessalonians 5:1-11 The Day Of The Lord.
As noted in the previous verses, Paul did not know the time of the Lord’s second coming, since he was open to the possibility that he himself might be alive at the time (4:15). Here Paul reiterates the same point, saying it would be like a thief coming in the night (vv. 1-2 Cf. II Pet. 3:10). It will be a day of judgment for those having a false security (v. 3 Cf. Is. 13:6-9). However, this day will not be as a thief coming in the night for the saints, for we look for this day in hope (v. 4). It will be a day of light and not darkness for the people of God (v. 5 Cf. Eph. 5:8; I Jn. 2:8). Therefore the saints are always awake and sober, on watch for the Lord (v. 6 Cf. Mt. 25:5). The unbeliever sleeps the sleep of death unawares (v. 7 Cf. Lk. 21:34). It is not the immanence of this day which keeps us alert, it is the unexpected nature of His coming, a day whose time no one can rightly predict.
Certainly, as regards our own deaths, any of us can be taken at any time, we do not need an immanence doctrine for this. Once again Paul turns to the triad of faith, love, and hope as that which is to motivate God’s people. Faith and love is our breastplate, and hope is our helmet of salvation (v. 8). For the saints this is not a day of judgment to eternal damnation, rather we will fully obtain the salvation that is in Christ Jesus (v. 9 Rom. 9:22-24; II Th. 2:13). We died with Him and to ourselves, and we live with and for Him (v. 10 Cf. II Cor. 5:15). Therefore we are to comfort and edify, or encourage, each other with these truths (v. 11). We should also note that the rapture spoken of in 4:17 will not happen before the Day of the Lord, for the Lord will return to the saints and unregenerate alike, for the former to complete salvation, and for the latter an unexpected final judgment.