Jamieson, Fausset & Brown

kingdom of God is not in word--Translate, as in Co1 4:19, to which the reference is "speech." Not empty "speeches," but the manifest "power" of the Spirit attests the presence of "the kingdom of God" (the reign of the Gospel spiritually), in a church or in an individual (compare Co1 2:1, Co1 2:4; Th1 1:5).