1 Thessalonians 3

1 Paul anxiously wanted to return to them to encourage and strengthen them. He probably had many other important things to teach them, but his ministry had been cut short when he was run out of town. Since the circumstances prevented Paul from gong personally, he sent Timothy. Apparently, the opposition was focused specifically at Paul, so Timothy would be able to return and minister with fewer difficulties.
2 Paul wanted the Thessalonians to have an unshakable, persistent faith in the presence of persecution. He trusted Timothy to be able to teach them how to rely on God during difficult times.
3 Christians today are not often taught to expect or endure persecution. Certainly, the world appreciates thoughtful, law-abiding citizens, but those who oppose Christianity do not make their judgements solely on these criteria. The mere fact that one believes the Bible and wants others to do the same makes worldly people defensive. The opposition may "persecute" Christians in small or large ways, from social snubbing to public execution. Jesus warned His followers that this would happen (John 15:19-16:4, 16:33), and He lived the experience Himself. Despite the fact that Jesus healed many people, sought to purify the worship of God, was hailed as Messiah among the masses, and found innocent under Roman law, the opposition still opposed and executed Him. When people become Christians, they seek to obey the principles of God, which His enemies vehemently oppose.
4 Paul had experienced this "natural" pattern of persecution himself, so he made sure to convey it as he preached. This is part of "counting the cost" of Christianity. It is only fair to warn people that Christians are promised hardships in this world, not ease. However, the hope of heaven, where there will be no more pain, sorrow, or persecution, makes faith completely worthwhile and suffering endurable.
5 Paul wanted to make sure that the Thessalonian's faith was strong. Persecuted people are distressed, and some might even consider their faith absurd if they were not prepared to suffer. Satan attempts to use suffering to dissuade people from faith, but God can use suffering to make our faith stronger. Times of affliction can serve to separate true believers from pretenders. If the Thessalonians were persisting in faith despite the persecution, it would be proof that God was living and working in them.
6 After Timothy returned, Paul made it a high priority to reply quickly by letter. Timothy had brought good news about the Thessalonian church, and Paul wanted to let them know that he was encouraged by them. Even under persecution, they had held to their faith in Christ and continued to love God and one another. Timothy also relayed that just as Paul sought to see the Thessalonians again, they likewise wanted to see him.
7 Paul and his missionary friends were also enduring persecution, so it was encouraging to him to hear about others that were enduring. The Holy Spirit helps even the newest of believers to hold to their faith in trying times.
8 It is through Christ that life has meaning and joy. We will still suffer in this world because sin still exists in it, but even so, we can experience the joy of knowing God and hope in the promise that one day He will do away with sin and its associated sorrows (James 1:2-4, 1 Pet 4:12-19).
9 Paul was so overjoyed with the Thessalonians that he felt his thanksgiving to God was inadequate.
10 The Thessalonians had been a pleasure to reach, and Paul continually asked God for the privilege of completing their training in the faith.
11 Paul ends this section with a prayer. His first recognizes God as Father and Jesus as Lord. This reminds us that Christians are in one spiritual family and under one divine authority. We are related and are to be fellow citizens in God's kingdom.

Paul then asks that God remove the obstacles that were hindering the missionaries from returning to Thessalonica.

12 God loves every person and made the way for each to be spiritually and physically renewed. Following His example, we are to care for the spiritual and physical welfare of others. In the church, that should be easier since we recognize our kinship and citizenship in Christ. We must work hard to nurture our relationships with one another so that the church will be strong and united. However, love is not to be confined to the church. Christians are to reach out to the community, just as God reached out to each of us before we accepted Him. Our hope is that people will respond to the love that God demonstrates through us so that they come to love Him as well. In that way, love continues to grow - and outgrow - the church.
13 The purpose of love is to keep us blameless before God. Jesus took away our sin, and the love He gives us helps us to behave as we ought towards one another. Jesus said that an active love for God and others was the foundation for all the laws and prophesies in Scripture (Mat 22:36-40). Therefore, if the foundational principle is followed, then the details (i.e., the specific laws) are naturally fulfilled (Rom 13:10).

When Jesus returns and the Rapture and Resurrection occur, He will present all Christians to God the Father. We are to be shown steadfast in our faith and loving towards Him and one another. These things please God. There is no greater prayer for someone else than what Paul concludes with here - that people find faith in God and the assurance of eternal life in Him, love and know Him, and love other people.