Thou, Thine, Thy, What does it mean?

As used in the King James Version of the Bible:

Thou – second person singular, nominative
Thee – second person singular, objective
Ye – second person plural, nominative
You – second person plural, objective

This is MY theory; it is MINE.
That is THY theory; it is THINE.

I would say it the other way around, that non-Catholic Christians don’t as a rule ask the saints to intercede for them. In the Mass, every prayer is directed as God, and it includes the Our Father since Christ told us to pray that way. Occasionally a Hail Mary will be added on a Marian feast day, and the litany of saints is included on Big days like the Easter Vigil. In addition to that, and not instead of that, folks do pray for intercession from Mary and the other saints.

I suppose they couldn’t have foreseen, the way the language would go; and from quite early on, Quakers became invested in their “thou / thee, etc.”, practice – a distinguishing thing.

I’ve always treasured the picture – possibly apocryphal – of William Penn meeting with King Charles II, for negotiation regarding settling parts of North America. For religio-political reasons, Charles had been hostile to Quakerism, and had thus had Penn to endure quite lengthy spells of imprisonment; but this wasn’t a “personal” thing. Penn – big on “no ostentatious respect for fellow-humans, all of us sinners” – insisted on continuing to wear his hat in the King’s presence, and addressing him as “friend Charles”, and – throughout – “thou”. Charles (in matters personal, a pretty laid-back monarch) just found Penn’s attitudinising comical, and let it all go by.