“These things have I spoken unto you, that my joy might remain in you, and that your joy might be full.” (John 15:11 KJV)
Joy… A cheerfulness, a calm delight, a gladness. Have you ever thought about joy? It is not a stationary object that you can possess like a trophy. So, if “joy” is ever to “remain in you” then it remains in the sense of an ever bubbling fountain. A cheerfulness not because you are locked in an artificial state of forcing yourself to be cheerful about something (or someone), but that there is an ever bubbling delight or gladness about the presence (or anticipated presence) of something (or someone) else. You can see how sorrow is at the opposite end of this. Likewise, sorrow is not the everpresent object itself, but it is the gloom or regret that seems to hang about about something (or someone) else.
Which brings an interesting realization… We can have neither joy nor sorrow if there is no “other”. No something (or someone) else. For those that are afraid of a let down, they can extinguish joy by reclusing inside. Same with those who want no sorrow. They can numb themselves to any “other”. So, “joy” and “sorrow” actually widen us! They make us bigger. Big enough that we can see that not only is there an “other”, but that “other” is relational and personal! Complex enough that we can have joy about one thing and sorrow about another because we now have a relational capability. The source of this joy now has a name and is known. He cares for us and by allowing a relationship with him, we can in turn have countless relationships with a whole bunch of “others”. Or as we do our best to extinguish that relationship with him, we find that all the other relationships turn very sour as well. Alas, it is true. We must love him and have a delight in him and in his presence that we might also be capable of loving another, and in that love for another our love for him is shown to be true.
“This is my commandment, That ye love one another, as I have loved you. Greater love hath no man than this, that a man lay down his life for his friends.” (John 15:12-13 KJV)