You became imitators of us, and of the Lord, having received the word in much affliction, with joy of the Holy Spirit,
With joy of the Holy Spirit ... Upon conversion, every Christian receives the earnest of the Holy Spirit; and the very first fruits of the Spirit are "love" and "joy"  (Galatians 5:22).  The overwhelming joy that attends one's obedience to the gospel is frequently mentioned in Acts, "he went on his way rejoicing" (Acts 8:39) being absolutely the normal experience following one's baptism into Christ.  That this initial joy of souls newly won in Christ is in evidence here appears in the fact of its being mentioned in connection with their reception of the gospel.