1 Corinthians 1:6
“Even as the testimony of Christ was confirmed in you.” Under the color of praises and thanksgiving he touches them sharply. “For not by heathen philosophy,” says he, neither by heathen discipline, but “the grace of God,” and by the “riches,” and the “knowledge,” and the “word” given by Him, were you enabled to learn the doctrines of the truth, and to be confirmed unto the testimony of the Lord; that is, unto the Gospel. For you had the benefit of many signs, many wonders, unspeakable grace, to make you receive the Gospel. If therefore you were established by signs and grace, why do you waver? Now these are the words of one both reproving, and at the same time prepossessing them in his favor.
Source: Homilies on First Corinthians (New Advent)