I think there is a difference between your own emotions / emotions of others and your own feelings / feeling of others. Emotions aint a thing noone can understand in a way for himself. But to be a master of feeling would be to see how all of the 4 named above are interconnected.
I through my relationship to my INFJ start to understand more about my own motivation. While I can explain rationally everything I do, there is infact sometimes more happening to me that I do not count in into the equations.
To master the bridge one day and to see motivation in others and now how they feel or what there emotions are, I think is far fetched in my case. But the ability to be aware of your emotions, understand the feeling and to put it in words for yourself is a thing I am gonna learn throughout my whole life.