Sentence:  ... you must follow the impulse of your own inspiration. If <small>THAT</small> commands the slaying of the victim, no bystander has a right to put out his hand to <WSD>stay</WSD> the sacrificial knife: but I hold you a stern priestess in these matters. 
Meaning of the word marked with <WSD> tags:  To restrain; withhold; check; stop.