Mark and Lottie (not their real names) had tied the knot more than 50 years ago. 
Their lives were laced together by years of raising children, enduring financial challenges, enjoying material successes, doting on grandchildren, and simply passing days together in the common rounds of meals and chores and holidays and vacations.
And then Lottie died.  The cancer came unexpectedly.  It all happened so quickly.  Everything changed for Mark.  The lights went out.
Mark sank lower and lower into sadness as the weeks passed. He spoke with me repeatedly about his loneliness and his sadness.  He did what people call “grief work.”  No light broke through the clouds for him.
One day my wife Joy (this is her real name) asked Mark to participate in our Youth-sponsored talent show at church.  She knew that Mark was an amateur dancer. 
Before Lottie had died, Mark used to go to the local elementary schools and teach the children about buck dancing, square dancing and tap dancing.  Since her death, Mark hadn’t thought the first thing about dancing.
To my complete surprise, Mark agreed to do his dancing and teaching routine for the talent show.

He was a little shaky as he started his performance, but he warmed to it quickly. As he danced, he was telling us about the origin and development of these dance forms.  His face brightened and the excitement in his voice rose with each step.

Several weeks later Mark shared with me that he had started going to the elementary schools again.  A popular local restaurant invited him to entertain guests while they waited to be seated.
I didn’t recognize the man telling me this.  The once sad man that I fully expected to follow his wife to the grave was smiling and laughing and looking forward to what life threw his way next.
This is what he told me.  “You know, Jake, as long as I focused on how much I missed Lottie and worked on getting over my sadness, I didn’t get anywhere.  But once I started thinking about doing things for other people, everything changed.  I still miss her.  But every time I start to fee low, I think about what I can do for somebody else, and it all turns back around for me.”
Mark taught me something that day about what Jesus meant when he told his disciples—when he told us—that we are salt and light.  (Matthew 5:13-16) 
Jesus came to serve.  He served you and me unto death on a cross.  Following him—taking up his cross—means to walk in the way of service.
So much writing on spirituality these days seems to focus on techniques for making myself more content or happier or more balanced or more integrated.
Certainly our Lord wants us to know his complete joy.  (Jn. 15: 11)  But the paradox is that we will never know the joy that the Lord desires for us as long as we set our hearts on attaining it.
Salt enlivens bland food.  Light illuminates dark spaces.  They each have a positive effect on something other than themselves in order to be themselves.
That’s what Jesus teaches us to do and what Mark learned in his grief.  The joy of the Lord comes to us when we set our hearts on the joy and justice and health of those around us.