Worries about the state of the community in Thessalonica made Paul to send to them Timothy. He is called “our brother and a fellow-coworker of God in the Gospel of Christ”. Paul is indicating that although he could not come himself, yet the one he sent is also very much dedicated to the Gospel.
The news about the persecution of Christian in Thessalonica becomes a reason for presenting a kind of theology of the Cross in the life of Christ’s followers. Suffering should be seen as something normal in a life of Christian. The apostle does explain the reasons for his ideas here, but in other places he speaks that it is a grace to suffer for Christ (Phil 1:29), it should even bring joy (Phil 2:17–18). In the case of Thessalonians sufferings and the joy in the Holy Spirit went together (1 Thess 1:6). In the 2 Cor 4:17), Paul even indicates that sufferings here will bring “more exceeding eternal weight of glory”.
Our life’s suffering and the cross contain with themselves “otherworldly”, eschatological dimension. There is not resurrection without the cross. In baptism, we die with Christ so we could rise with Him and live for God. Thus, baptismal connection of death and resurrection will take an eternal character, when after dying in this world, we move to live with God for eternity.
Theology is one thing and life is another thing. Paul knows well that under severe pressure from the world even the best theology can crumble. That is the reason for the mission of Timothy. It is one thing to know that “we should suffer tribulations” (1 Thess 3:3) and another one to actually suffer those tribulations. A believer under pressure can give up their faith. In verse 5, Paul refers to Gen chapter 3, where the Eve was successfully tempted by the snake. Paul worried that he had succeeded again in Thessalonica. Thus the news that all is well in Thessalonica brought relief and joy to the apostle.
What brings the apostle so much joy? Their faith and love. These two theological virtue are of outmost importance, actually the most important ones: faith in God and mutual love. In the letter to the Galatians, Paul connects them together stating that the only thing that matters in Christian life is “faith acting through love” (Gal 5:6).
In this passage, we also notice that missionaries also need to see the fruits of their labor. The good news brought by Timothy gave Paul not only joy but also an encouragement to continue his missionary activity. The joy that Paul felt upon hearing the news from Timothy comes from God and is expressed before God in prayer.
Finally, since now Paul does not worry about a possibility of being deceived by the tempter like Eve in the garden of Eden (1 Thess 3:5), he presents another reason for coming: to perfect what is [still] lacking in their faith (1 Thess 3:10). The apostle, however, does not set a concrete date for his coming. He leaves it entirely in God’s providence. In 1 Thess 2:18, Paul said that it was Satan, who hindered his coming to them. Now, he trusts that “God, our Father and Jesus, our Lord” will overcome that hindrance and will direct “our way” towards them.
Chapter 3 ends with a wish for the community in Thessalonica expressed in the form of prayer. Paul wants the community to (1) increase in numbers; (2) to exceed in love; (3) to be established in holiness. The one who does the increasing is the Lord. It is also He who can make their love to excel. This love - agape - has two dimensions: towards the members of the community - internal, and towards all [people] - external.
Regarding third aspect, Paul will say something concrete about “holiness” in chapter 4:1–11. Here, Paul has in mind God’s commandment, “be holy for I am holy”, given to the people of Israel. This commandment is mentioned three times in the book of Leviticus (Lev 11:44; 19:2; 20:7). The meaning of holiness there is very practical, namely, avoiding sins and obeying God’s commandments. Again, it is the Lord himself who, Paul prays, establishes them in holiness.
In the Old Testament the word “saint” referred to the angels alone (see Ps 89:6,8; Job 5:1; 15:15; Daniel 8:13). For the apostle, the saints are all the just ones, justified by God and living a holy life. Paul often uses this word to address the members of a Christian community (Rom 1:7; and 1 Cor 1:2; Phil 1:1). In verse 13, all the saints of Christ probably still refers to the angelic beings (see Matt 25:31; and also 1 Thess 4:16–17).
Paul ends chapter 3 in a similar way like chapter 1. For the second time, we hear about “the coming of our Lord Jesus Christ” (1 Thess 3:13; 1:10). This coming of the Lord will be explained in chapter 4.