That’s the old school phrase for “Pay it forward”. I started many generations ago, and most likely when people started writing letters.
“Send a letter to get a letter” conveyed message is that you must first do…in order for anything to be received.
Newton’s 3rd law of motion even states: “Every action has an equal and opposite reaction”.
So just start the action and see what happens.
– Dr. Vik, The Culture King