"Our-great-loss-". What is the loss? How has it been caused? What would they do to make up the loss?

The loss that Mr. and Mrs. White had been talking about was the death of their only son Herbert. Although he died in an accident where he got caught up in a machine, but the actual cause of his death was the monkey's paw, to which the Whites had made a wish. The paw was cursed and was said to bring destruction to its owner as a penalty for tampering with fate, although it granted the wish as well. Herbert's death came as their penalty for the 200 Pounds that they had asked for in their first wish.

To make up for the loss, the Whites decided to make another wish of making their son alive again, but Mr. White's premonition of Herbert coming back alive as a decayed and decomposed body seemed to be coming true, and it led to him making his third and final wish of having him dead and at peace.