Albert Barnes Commentary 1 John 1:4

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

And these things write we unto you. These things concern Him who was manifested in the flesh, and the results which flow from that.

That your joy may be full. This is almost the same language that the Savior used when addressing His disciples as He was about to leave them (John 15:11), and there can be little doubt that John had that declaration in remembrance when he uttered this remark.

The meaning here is that full and clear views of the Lord Jesus, and the fellowship with Him and with each other which would follow from that, would be a source of happiness. Their joy would be complete if they had that; for their real happiness was to be found in their Savior. The best editions of the Greek Testament now read "your joy," instead of the common reading "our joy."