Citation de Zebraman
I know that, but Thy is mostly used to refer to god, since everyone became You in english. But Blake poetry also incorporate a lot of his own mythology and metaphysics.
>>Zebraman
I know that, but Thy is mostly used to refer to god, since everyone became You in english. But Blake poetry also incorporate a lot of his own mythology and metaphysics.

That's not quite right. Actually, it's the opposite: God is mostly adressed –and not referred to– as thy, but thy is used in many other contexts, chiefly humour, in some dialects it still is the main personal pronoun of the second person.
Your confusion most likely stems from the fact that when someone wish to mimick and mock the church or bigots, they often use a very archaic English, including thou, thy, thine, brethren, myne, verbs ending in -yed, -st or -est, etc.
Or it could also be due to the hegemony of the King James, whose language is rather dated, I can't be sure.
Anyways, in this specific case, thy is aimed at the tyger itself, which I find obvious.

That being said, Blake does speak of God, or at least of a demiurgic figure, when he writes he or immortal hand and eye. And given that he writes of the one who made the lamb I'd daresay there's got to be some link in his mind with god of christians. If nothing else, he's using the common imagery to his benefit.