Why 'which' and not 'who'
From the Oxford English Dictionary (requires subscription)
Which...
I 2 b. Also (Old English and occasionally later) = Who. Obsolete except as a dialect or humorous substitute for what.
In King James Bible it's indeed "which was", but in its 21st century edition it's "who was", so you are correct in saying that it is an ancient usage, and would not be correct in modern English.
However, there is one instance when you can refer to a person using "which": if it's followed by a noun.
You decide which doctor is right for you.
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