1-3: Paul was extremely thankful to God for the Thessalonians and their works.
4-10: Paul knew the Thessalonians were predestined to receive the Christ because they were convicted by the Gospel, repented from idolatry, and they lived holy lives imitating Jesus and the disciples. Their dramatic conversion became known in Macedonia and Achaia, then throughout the world.
1-2: Although Paul was treated poorly and imprisoned in Philippi, he remained bold in sharing the Gospel with the Thessalonians. They received Christ as a result so his efforts were not in vain.
3-8: Paul, Silvanus, and Timothy had pure motives in preaching the Gospel. They didn't deceive, use flattery, seek glory from people, or financial gain. Instead, they sought to please God, share the Gospel, and care for the Thessalonians.
9-12: Paul reminded them how of he and his disciples worked day and night so they wouldn't be a burden to the Thessalonians during their visit.
13: The Thessalonians correctly recognized Paul's message to them as the word of God.
14-16: Paul was speaking of a specific group of Jews (those who delivered Jesus over to Pilate), not their entire race or all members of the Jewish religion. Some have tried to misconstrue this passage as anti-Semitic but their case makes little sense when you consider that Paul himself was a Jew who worshipped a a risen Jewish rabbi, and said he wished he could be "accursed, cut off from Christ" rather than the Jews. He is, in effect, saying he would rather suffer the consequences of God's judgment rather than see the Jews face it.
17-20: Scripture not clear how Satan hindered Paul from coming to Thessalonica.
1-5: The Christians in Thessalonica were being persecuted (Verse 2:14) for their faith. Paul sent Timothy to encourage them and report how they were doing. Part of his encouragement was the knowledge God, in his foresight, destined them to face these afflictions (verse 3) so they shouldn't be moved in their faith. While this may not seem comforting, it teaches that God is sovereign over the situation and our suffering is not in vain. In the end, it glorifies God and helps us grow in spiritual maturity.
6-13: Timothy returned to Paul with an encouraging report that they were standing strong in their faith despite being persecuted. This brought Paul comfort in his own situation of persecution.
1-8 God's will for our lives is sanctification—abstaining from sexual immorality and controlling our bodies for honorable use. After we are redeemed by God through Jesus, we begin the process of sanctification and continue throughout our lives.
9-12: The Thessalonian Christians were loving toward one another but Paul encouraged them to do so even more. He also encouraged the to live a simple, quiet life of work and financial independence so outsiders wouldn't be burdened by them.
13-18: We shouldn't grieve over the death of fellow Christians the way unbelievers do. When Jesus returns, everyone who trusted in Christ will be resurrected and Christians who are alive will even before those who are alive will be gathered up and transformed into their heavenly bodies. Therefore, we will be with our deceased loved ones and the Lord forever.
1-8: The Day of the Lord (Christ's return and judgement of mankind) will come at a day and time that no one expects. We should live in sober realization of this fact. Paul uses a few metaphors for spiritual conditions. Unbelievers are in spiritual sleeping, drunken state, ignorant of spiritual realities. In contrast, believers are spiritually aware (awake) and sober, acknowledging spiritual realities and the coming judgement.
9-11: The awake/sleep metaphor switches to the one used in verse 4:14, referring to life and death rather than spiritual blindness. We should encourage one another with the news that Jesus died for us so we wouldn't have to face God's wrath.
12-22: Paul gives some brief, final instructions to the church that are just as relevant today. They are straightforward commands that deal with a variety of different situations and people in the church.
23-24: God promises to sanctity us completely so we are blameless when Jesus returns. No matter how much we've sinned, Jesus makes us completely pure and guiltless in God's sight. All of our sins were dealt with on the cross and gave us Jesus' righteousness. In addition, we are also being sanctified in living out the Christian life. We are not perfect, but if we have the Holy Spirit, we will continue to grow in holiness through trials.
25-28: Paul closes with further instructions to the Thessalonians, including reading this letter to all of the Christians.