“So then” (Ἄρα οὖν) is a common Pauline way of drawing a logical conclusion to a section. Since his readers have been chosen by God as the first to share in the Gospel, they will be glorified at the time of Christ’s return (2:14). If this is true, then they ought to respond to this reality in the following two ways:
First, the Thessalonians are to “stand firm” (στήκω). This verb has the sense of being firmly committed to something (BDAG). This stands in contrast to Paul’s description of the church at the beginning of this chapter: they were unsettled and alarmed by a report that then Day of the Lord already come. Rather than be shaken by the teaching which contradicted what Paul had taught them, they ought to stand firm in what they know to be the truth.
Second, the readers are told to “hold on” (κρατέω) to the traditions Paul has passed along to them when he was with them or by his earlier letter. Once again, this is necessary since it is possible the disturbing report came to the church from a letter claiming to be in Paul’s name. In 1 Thessalonians Paul was very clear his appeal to the church was not motivated by greed nor was he using rhetoric to fool them into believing something which was not true.
It is very important to notice here that Paul says he passed along traditions (τὰς παραδόσεις). This implies there was a body of teaching Paul could “hand down” to his churches, some of which Paul says he had received from those who were before him. This includes teachings about the Lord’s Supper (1 Cor 11:23) and the resurrection (1 Cor 15:3-5). Although there are some things Paul says he received from the Lord directly (1 Thess 4:15), others are part of a growing doctrinal and ethical tradition Paul delivers to his churches and expects them to hand down to the next generation of believers.
Third, Paul tells the Thessalonians to be encouraged and strengthened in both deed and word (2:16-17). This benediction is something of a conclusion to the first part of the letter. The benediction in 2:16-17 is a prayer to the Lord himself to give the readers strength to hold on to Paul’s teaching. There are two parts to Paul’s wish for the church. First, “Encourage your heart…” This is an inward action, although “encourage” might be a bit soft. In 3:12, Paul uses the same verb to strengthen a command (translated “we urge.”) What is in mind is the Lord prodding and urging the heart to keep the command to hold tight to the teachings Paul gave them.
Second, Paul prays that the Lord would strengthen his readers. This is an external action, an enablement to do the action commanded. Even if the Lord nudges you to do the right thing, it is still possible for you to ignore that urging. The point of this part of the prayer is to actually follow through and do what must be done.
The encouraging and strengthening is to be done “in deed and word.” There is a relationship here “between inward encouragement and outward behavior.” (Wanamaker, 1-2 Thessalonians, 272). Paul does not want his congregation to say one thing and do another.
This section of 2 Thessalonians has some very real application to the modern church. There are occasionally strange teachings which do not conform to the “traditions handed down” and cause some in the church to be unsettled or alarmed. The recent weirdness about the solar eclipse is a case in point. Even a few reasonable people I know were seriously considering this as a “sign of the end.” (Short answer: it was not a sign of the end). Sometimes a popular writer will publish a book with a new or radical reading of Scripture, the church ought to evaluate it in the light of the “traditions handed down.” But from a contemporary perspective, what are those traditions? Is this just Scripture? The Nicene Creed? Do denominational commitments matter? How does the church strengthen itself so that it can stand firm and hold fast to the “traditions handed down” yet still respond to a culture where traditions like this are meaningless?