Here is a list of resources for further study into the Gospel of John and the letters of 1, 2, and 3 John.
SERMONS
Sermon on the context of the Gospel of John
Sermon podcast on 2 and 3 John
VIDEOS
Bible Project: How to Read The Bible: NT Letters historical context ep. 2
Bible Project: How to Read The Bible: NT Letters literary context ep. 3
Bible Project: Overview of John part 1
Bible Project: Overview of John part 2
Bible Project: Overview of 1, 2, 3 John
PODCASTS
Knowing Faith: Union with Christ
Knowing Faith: What is the Church?
ARTICLES
BOOKS
The Letters of John: An Introduction and Commentary by John R. W. Stott
Cornerstone Biblical Commentary, Vol 13: John and 1, 2, and 3 John by Grant Osborne and Philip W. Comfort
The New American Commentary: 1, 2, 3 John, vol. 38 by Daniel L. Akin