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.
Not in word only ...  Paul's preaching was accompanied by the exhibition of miraculous apostolic powers  (Romans 15:19) of "signs and wonders and mighty deeds in the Holy Spirit"; such things, of course, having been the Father's way of confirming the gospel he preached.