and that our Gospel came to you not in word only, but also in power, and in the Holy Spirit, and with much assurance. You know what kind of men we showed ourselves to be among you for your sake.
and in much assurance: This phrase is further descriptive of Paul. As Vincent notes, it is "Assured persuasion of the preacher that the message was divine" (Vol. IV 17). The success of Paul’s preaching at Thessalonica may have been largely attributable to the confidence he exhibits in the message he proclaims.