It’s impossible to improve upon this passage by commentary, but I offer an unfamiliar translation (by J. B. Phillips) of a simple and very familiar text:
“Now I am giving you a new command—love one another. Just as I have loved you, so you must love one another. This is how all men will know that you are my disciples, because you have such love for one another.”
The test of discipleship isn’t, it turns out, whether you accept the Nicene doctrine of the Trinity, despise Joseph Smith, or reject the Book of Mormon.