To complete her joy
Joy (and happiness for that matter) is completed when it is expressed. When something good happens, or even when I am given a godly perspective in the midst of great pain, I have a burning desire to share it with those that I love and even God Himself. It just seems so silly to tell God about what just happened or how I am relying on Him in the midst of great trial as if I am clueing Him into something that He doesn't, already, know. But He puts up with it doesn't He? He even desires it because He desires my good. He knows that it is good for me to complete my joy (and even my happiness) through expressing that back to Him. That is one of the reasons why it is so good for me to worship my God by reflecting back to Him all that He is to me. As I articulate the joy I feel as a result of who He is my greatest good is achieved. My joy goes all the way down and it sinks deep into the earth as a most suitable foundation.
I was, recently, on a business trip with a woman who was completely enamored with a new grandson. Mind you I really like children but she said that she was going to "wear me out" with how much she talked about him (she almost did). But, I was fine with that because I knew that there was a desire on her part to complete her joy and happiness by sharing it with me. That I was receptive to it and asked her questions about her grandson made it more likely that she would share more with me...and she did. Yet, I was glad to oblige because, well, that is exactly what my God does for me. And I want to be like Him.
Oh, God, do I want to be like you.