In the last verse of the preceding section John has concluded that if we love one another, two things may be said to follow: first, that God abides in us, and second, that God’s love is perfected in us. These two conclusions give the outline for the next two sections of this chapter. In the first section (vv. 13-16) God’s indwelling of the Christian is discussed in greater detail; in the second (vv. 17-21) the perfection of love is analyzed. That the indwelling of the Christian by God is the theme of the first section is evident from the threefold repetition of the idea: once in verse 13 (“we dwell in him, and he in us”), once in verse 15 (“God dwelleth in him, and he in God”), and once in verse 16 (“He that dwelleth in love dwelleth in God, and God in him”).
It is not easy to give a simple outline to this section of the chapter, as it was, for instance, for verses 7-12 on the basis of the three-fold repetition of the phrase “love one another.” Still, the major ideas are obvious. First, we know that we dwell in God and God in us because of the Spirit, whom He has given to us (v. 13). Then, second, we know that He has given us the Spirit because we have come to believe in Christ and love the brethren (vv. 14-16).
John’s first point is that believers know that they dwell in God and God in them because of the Holy Spirit, whom God has given to them. By this John emphasizes that God is always first in spiritual things and that apart from His gracious activity by the Holy Spirit to open blind eyes to perceive the truth and move rebellious wills to turn from sin to the Savior, no one would believe in Christ or love the brethren. In the next few verses John is going to talk of belief in Christ and love of the brethren, but we must not think, as some commentators have, that these are conditions by which we are enabled to dwell in God or remain in Him. To believe in Christ and to love the brethren are not conditions by which we may dwell in God but rather are evidences of the fact that God has already taken possession of our lives to make this possible.
This leads directly to John’s next point. For, having said that it is always God who is first in spiritual things, the question with which he next wants to deal is this: “Is God thus at work spiritually in me?” In answer to this question he, therefore, now argues that if God is at work the evidences for it will be seen in a combination of love and sound doctrine. In other words, we may know that we have the Spirit because we have come to confess Christ and dwell in love.