The Thessalonians are given to understand both how mindful of them Paul was at all times in thanksgiving and prayer, 1-4; and also how well he was persuaded of the truth and sincerity of their faith and conversion to God, 5-10.
1 Paul, Silvanus, and Timothy, to the church of the Thessalonians which is in God the Father and in the Lord Jesus Christ: Grace to you and peace from God our Father and the Lord Jesus Christ.
2 We give thanks to God always for you all, making mention of you in our prayers, 3 Remembering without ceasing your work of faith, labor of love, and patience of hope in our Lord Jesus Christ in the sight of God and our Father, 4 Knowing, brothers beloved by God, your election. 5 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 manner of men we were among you for your sake. 6 And you became followers of us and of the Lord, having received the word in much affliction with joy from the Holy Spirit, 7 So that you were examples to all who believe in Macedonia and Achaia. 8 For from you sounded out the word of the Lord, not only in Macedonia and Achaia, but also in every place your faith toward God is spread abroad so that we do not need to speak anything. 9 For they themselves report concerning us what manner of entering in we had to you and how you turned to God from idols to serve the living and true God, 10 And to wait for his Son from heaven, whom he raised from the dead, even Jesus who delivered us from the wrath to come.
Matthew Henry Commentary - 1st Thessalonians, Chapter 1[➚]
[v.6] - "with joy from the Holy Spirit" - From the Pulpit Commentary: "That is, not merely spiritual joy, or joy in the Holy Spirit, but joy which proceeds from the Holy Spirit—joy which is produced by him, of which he is the Author."
[v.9] - "what manner of entering in" - From the Pulpit Commentary: "'Entering' here evidently refers, not merely to the outward entrance, the mere preaching of the gospel among the Thessalonians; but to the access, the internal entrance, which the gospel found into their hearts; that is, with what power and fullness of the Holy Spirit we preached the gospel to you, and with what joy and confidence and contempt of danger you received it."