1 Thessalonians read the whole chapter 1.
vv.5-6, “For our gospel did not come to you in word only, but also in power, and in the Holy Spirit and in much assurance, as you know what kind of men we were among you for your sake. And you became followers of us and of the Lord, having received the word in much affliction, with joy of the Holy Spirit.”
The Thessalonians were idol worshippers, upon receiving the Gospel they turned away from following idols. Gospel preached with demonstration of Holy Spirit and power produced much conviction or assurance in their hearts. These believers suffered afflictions for their newfound faith, yet not without joy from the Holy Spirit. Paul speaks of their faith (tried and tested through the fiery furnace of afflictions) as exemplary and worthy of emulating.
We desperately need this type of change-producing Gospel, turning people from their dead beliefs and ways to the living GOD and His Son, Jesus. Exemplary faith comes by the authentic word of GOD through the convicting power of the Holy Spirit, and is full of joy in the face of adversity. This is daily winning recipe: the word of GOD through the power of the Holy Spirit producing much assurance in the heart with results of faith following and lives changing to the glory of GOD and His Christ.