1 John 4:12-17 is organized as a chiasm:

A. No one beheld God, 12a
B. Mutual love, God abides, love perfected, 12b
C. Abiding in God, He in us, 13
D. Bear witness to the Savior, 14
D’. Confessing that Jesus is Son, 15a
C’. God abides in him, he in us, 15b
B’. God’s love for us, abiding in God, love perfected, 16-17a
A’. As He is, we are in the world, 17b

At the same time, another structure overlaps and intertwines this one:

A. God’s love for us, 16
B. Love perfected, 17a
C. Confidence in judgment, 17b
D. As He is, we are in the world, 17c
C’. No fear in love, 18a
B’. Perfect love casts out fear, 18b
A’. We love before He loved us, 19

These intertwined chiasms are framed by verses 12 and 20: “No one has beheld God” is answered by v 20: “the one who does not love his brother whom he has seen cannot love God whom he has not seen.” So, verses 12-20 (or perhaps 21) form a larger unit within interlocking chiasms between.

This structure reinforced one great theme of the whole passage. A and A’ in the first chiasm (12a and 17b) make an intriguing match, and the importance of this theme is highlighted by the fact that 17b (c) is also the center of the second chiasm. The “problem” of God’s invisibility is answered by mutual love. This is also the theme of the outer frame of the whole passage: No one has seen God, and our love for God is visible in our love for the brothers. This works because “we” are in the world what God is. The Word has manifested Himself in flesh (1:1-4; 4:14), and by our union with the Word-made-flesh we are the visibility of the invisible God. Specifically, the invisible God who is love manifests Himself in Jesus and in the love of the body of Christ.