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 the Holy Ghost: This is very likely a reference to the fact that Paul speaks by inspiration. "But I certify you, brethren, that the gospel which was preached of me is not after man. For I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ" (Galatians 1:11-12).