John Calvin Commentary 1 John 1:4

"and these things we write, that our joy may be made full." — 1 John 1:4 (ASV)

That your joy may be full. By "full joy," he expresses more clearly the complete and perfect happiness that we obtain through the Gospel; at the same time, he reminds the faithful where they ought to fix all their affections. True is that saying:

Where your treasure is, there will be your heart also (Matthew 6:21).

Whosoever, then, really perceives what fellowship with God is, will be satisfied with it alone, and will no more burn with desires for other things.

The Lord is my cup, says David, and my heritage; the lines have fallen for me on an excellent lot (Psalms 16:5–6).

In the same manner does Paul declare that all things were deemed by him as dung in comparison with Christ alone (Philippians 3:8). He, therefore, who considers himself happy in having communion with God and acquiesces in that alone, has finally gained proficiency in the Gospel; and thus he prefers it to the whole world, so that he is ready for its sake to relinquish all other things.