For the kingdom of God - The reign of God in the church (see the note at Matthew 3:2); meaning here, probably, the power or authority which was to be exercised in the government and discipline of the church. Or it may refer to the manner in which the church had been established. “It has not been set up by empty boasting; by pompous pretensions; by confident assertions. Such empty boasts would do little in the great work of founding, governing, and preserving the church and unless people have some higher powers than this they are not qualified to be religious teachers and guides.”
But in power -
(1) In the miraculous power by which the church was established - the power of the Saviour and of the apostles in working miracles.
(2) In the power of the Holy Spirit in the gift of tongues, and in his influence on the heart in converting people; see the note at 1 Corinthians 1:18.
(3) In the continual power which is needful to protect, defend, and govern the church. Unless teachers showed that they had such power, they were not qualified for their office.