<p>4:15 <em>Whoever shall confess that Jesus is the Son of God, God abides in him and he in God</em>- As noted on :2 and :3, confession was required, not just secret 'belief'; and such confession meant being put out of the synagogues and thereby out of the Jewish world / society. Therefore many 'believed' but would not &quot;confess&quot; (Jn. 9:22; 12:42); see on 2:23. God's abiding in a person is through the Spirit (:13). And yet the Comforter passages promise that the indwelling spirit will empower our witness or confession. This therefore is another evidence of having received the Spirit; that we shall testify, in the power of the Spirit. The false teachers and infiltrators didn't do so; and were not therefore &quot;of God&quot; and their claims to Spirit possession were false.</p><p>There is a repeated Biblical theme that the believer's relationship with the Father is essentially <em>mutual</em>. For example, we dwell in God (Ps. 90:1), and He dwells in us (1 Cor. 3:16). And here too: &quot;God abides in him and he in God&quot;. We work out our salvation, and God in response works in us both to will and to work (Phil. 2:12,13 RV). This is the mutuality which arises from the Spirit.</p>