I’m already in the Army

A friend was in front of me coming out of Shul one day, and the Rabbi was standing at the door as he always is to shake hands. He grabbed my friend by the hand and pulled him aside.
The Rabbi said to him, “You need to join the Army of G.d!”
My friend replied, “I’m already in the Army of G.d, Rabbi.”
The Rabbi questioned, “How come I don’t see you except at Yom Kippur and Yizkor?”
He whispered back, “I’m in the secret service.”