what new quality did santiago possess for the eventual big catch?

I am not sure what quality you are looking for. Santiago is always hoping to have success when he fishes; he believes that today could be his lucky day, and even though he is without the boy, he believes he could win. At one point, he talks his "hands" into letting him use them to catch the fish; he even promises religious prayers such as the Our Father and the Hail Mary for success in the ocean.