I always loved hearing this gem from church history about the end of the apostle John's life:
(From biblepath.com) There is a church tradition, which says, that when John was evidently an old man in Ephesus, he had to be carried to the church in the arms of his disciples. At these meetings, he was accustomed to say no more than, "Little children, love one another!" After a time, the disciples wearied at always hearing the same words, asked, "Master, why do you always say this?" "It is the Lord's command," was his reply. "And if this alone be done, it is enough!"
John's disciples could certainly be forgiven (and I have no doubt that he himself would forgive them!) for thinking the apostle was a "Johnny One Note." How many times have we heard him exhort, "Love one another?"
We encounter it again in vs. 7 directly, and in many other places in this chapter indirectly. It is quite clear that John felt this was an essential message. He stressed it again and again. And why not? If you had to boil down Jesus' teaching into one bullet point, you could do far worse than "Love one another." Jesus Himself, when asked about the greatest commandment, cited love of God and love of neighbor.
The Christian life must be based on, and continually return to, the central act of love. It matters little else what we do (See I Corinthians 13) if we have not love. So while John may be guilty of being a "Johnny One Note" at times, it is a good note to sing.
I was struck by vs. 5-6. It seems like such a strong echo of John's Gospel.
I John 4:5-6: "They are from the world and therefore speak from the viewpoint of the world, and the world listens to them. We are from God, and whoever knows God listens to us, but whoever is not from God does not listen to us."
John 8:23: "You are from below; I am from above."
John 8:42-44: "If God were your Father, you would love me, for I came from God and now am here...Why is my language not clear to you? Because you are unable to hear what I say. You belong to your father, the devil..."
John 10:27: "My sheep listen to my voice; I know them and they follow me."
The major difference I see is that what was first person singular in the Gospel of John ("I," "me") has become first person plural in I John ("We," "us")!