Would you please tell me what is the meaning of Yours in Christ in the end of letters.



It's a closing rather like Yours sincerely. It is used by some devout Christians.

It's formulaic, so the recipient is unlikely to carefully analyze the meaning.


"Yours" is a common component of a complimentary close, as in "Sincerely yours". It is a meaningless polite formality. "In" in your example is an antiquated use denoting mystical union with its object. This use of "in" is so rare today that you won't see it in ordinary dictionaries. "Yours in Christ" basically means "We are both devout Christians."