The Epistles of John, assigned to the writer of the Fourth Gospel and the Revelation, testify that God is love and that love is the test of religion. Second John is written to “the elect lady and her children,” probably a church; Third John is addressed to “the beloved Gaius.”

1 John 4

4:6 We are of God: he that knoweth God heareth us; he that is not of God heareth not us. Hereby know we the spirit of truth, and the spirit of error.