In brief? Because honoring a day of rest is, I think, a yogic way of living life.
Sabbath is the Christian tradition of not working one day a week. In the beginning, God worked six days and rested one. God also commanded, “Remember the Sabbath, to keep it holy.” Sabbath is a day a week to experience God’s rest. It is a weekly rhythm not to prevent us from doing work, but to free us from trying to do everything.
Savasana is the yoga pose usually performed at the end of class. Savasana consists of “relaxation pose” or “corpse pose”: lying flat on the floor, doing nothing but breathing. To me, it is the essence of yoga–rest.
If I picture myself “living my yoga,” as the popular phrase says, I might think about my week and how it might compare to a yoga class. The six days are the class with its poses. Sabbath, then, is resting in a lived Savasana – a day in which I do not do my other working poses. I don’t write, I don’t teach, I don’t prep for teaching. Instead, I’ll read a novel, or play a board game, or watch a movie, or have friends over for dinner.
So Sabbath Savasana is just a picture of whatever my Sabbath activity is that week. Taking a picture is just another way to honor it.