You did not kill the fish only to keep alive and to sell for food, he thought. You killed him for pride and because you are a fisherman. You loved him when he was alive and you loved him after. If you love him, it is not a sin to kill him. Or is it more?
As Santiago sails back to his village on the fourth day of the novella, towing behind him the carcass of the decimated marlin, he tries to make sense of the destruction he has witnessed. He feels deeply apologetic toward the fish, which he sees as too dignified for such a wasteful end. He attempts to explain to himself his reasons for killing the fish, and admits that his desire to hunt the fish stemmed from the very same quality that led to its eventual destruction: his pride. He then justifies his behavior by claiming that his slaying of the marlin was necessitated by his love and respect for it. Indeed, when Santiago kills the fish, the loss of life is somehow transcendently beautiful, as opposed to the bold, senseless scavenging on the part of the sharks.