1 Finally, brothers, we earnestly ask and exhort you in the Lord Jesus that, as you received from us how you should conduct yourselves to please God--and as you are conducting yourselves--you do so even more.
2 For you know what instructions 1 we gave you through the Lord Jesus.
3 2 This is the will of God, your holiness: that you refrain from immorality,
7 For God did not call us to impurity but to holiness.
13 We do not want you to be unaware, brothers, about those who have fallen asleep, so that you may not grieve like the rest, who have no hope.
15 Indeed, we tell you this, on the word of the Lord, that we who are alive, who are left until the coming of the Lord, 3 will surely not precede those who have fallen asleep.
17 Then we who are alive, who are left, will be caught up together 4 with them in the clouds to meet the Lord in the air. Thus we shall always be with the Lord.
1  Instructions: these include specific guidelines on the basis of the Lord's authority, not necessarily sayings Jesus actually uttered. More profoundly, as 1 Thes 4:8 implies, the instructions are practical principles that Paul worked out in accordance with his understanding of the role of the Spirit.
2 [3-8] Many think that this passage deals with a variety of moral regulations (fornication, adultery, sharp business practices). It can be more specifically interpreted as bringing general norms to bear on a specific problem, namely, marriage within degrees of consanguinity (as between uncle and niece) forbidden in Jewish law but allowed according to a Greek heiress law, which would insure retention of an inheritance within the family and perhaps thereby occasion divorce. In that case, "immorality" (1 Thes 4:3) should be rendered as "unlawful marriage" and "this matter" (1 Thes 4:6) as "a lawsuit." The phrase in 1 Thes 4:4, "acquire a wife for himself," has often been interpreted to mean "control one's body."
3  Coming of the Lord: Paul here assumes that the second coming, or parousia, will occur within his own lifetime but insists that the time or season is unknown (1 Thes 5:1-2). Nevertheless, the most important aspect of the parousia for him was the fulfillment of union with Christ. His pastoral exhortation focuses first on hope for the departed faithful, then (1 Thes 5:1-3) on the need of preparedness for those who have to achieve their goal.
4  Will be caught up together: literally, snatched up, carried off; cf 2 Cor 12:2; Rev 12:5. From the Latin verb here used, rapiemur, has come the idea of "the rapture," when believers will be transported away from the woes of the world; this construction combines this verse with Matthew 24:40-41 (see the note there) // Luke 17:34-35 and passages from Revelation in a scheme of millennial dispensationalism.