The first thing I notice is that the suffering of Philippi (Acts 16:22-24) was used by God to make Paul and his team more confident to preach the gospel in Thessalonica. God did not waste the opposition. It had a distilling effect on his motives and emboldened him for the central task.
The model of ministry set forth in 1 Thessalonians 2:7-12 is precious. Like a nursing mother. . . like a father. The reason ministry worked that way is that they were dear to him (v.8). No wonder the church grew from only three weeks worth of initial work (Acts 17:1-2).
The church received God's word as from God, not men and were encouraged to walk worthy of the call of God (1 Thess. 2:12-13). That's the other reason the church thrived after only three weeks.