Question: You said that it is necessary to invest a small amount of effort to feel my joy in another. What does “a small amount of effort” mean?
Answer: Describe to yourself a state like this, that you now find yourself with feelings and thoughts about another and want to see him joyful, happy, and fulfilled. And now think about what you could do to attain this. This will bring you to the possibility of acting in some way for the sake of a friend.
You need to learn what makes him happy, exactly what he needs, and in this way you combine his desire to yours, and his desire becomes yours. That is to say you have already acquired another part of your soul.
From the Conventions in Krasnoyarsk 6/16/13, Lesson 5