The god chuckled and the sea around him vibrated with the energy of his glee. "You are a good person, Jake Sully. Someone has to see that good things happen to good people." And he was the only one left of his pantheon. His family. His allies.
Of course, this would have all had way more mystery to it if Kai had not identified himself as the source. But his old ways did not work as well anymore and unlike the Christian god, he was not opposed to direct contact with mortals.
"Now pick a form and we will swim. Unless you want me to choose."