PREPOSITIONS. Of in adjurations, &c.Of hence is used in appeals and adjurations to signify "out of."
Hence, the sense of "out of" being lost, = "for the sake of," "by."
“Of charity, what kin are you to me?
“Speak of all loves.
Similar is the use of of in protestations:
“Let it not enter in your mind, of love.
“Leon. We'll have dancing afterwards.
Ben. First, of my word.
“A proper man, of mine honour.