It would have been better for them not to have known the way of righteousness than to have known it and then to turn away from the holy commandment passed on to them.
KJV
For it had been better for them not to have known the way of righteousness, than, after they have known [it], to turn from the holy commandment delivered unto them.
ASV
For it were better for them not to have known the way of righteousness, than, after knowing it, to turn back from the holy commandment delivered unto them.