Lostpedia tries to translate the words CrazyMom speaks when presenting the wine to Jacob to become the new island guardian:
"For we do not accept this just as a common drink, but as if that (he?) should be one with me."
This solemn statement gives us no insight on what, if anything, CrazyMom was giving Jacob. The symbolism, if any, is lost in that scene.
I had thought the words were a "magic spell" that would grant Jacob full powers over the island as its protector. But that is not the case. It is another non-answer to the question of what is the island.