I am confused as to whether the word "fret" is considered archaic. I'd settle on "used more often 100 years ago" or something similar, but I have doubts and curiosity.
I don't think its archaic but it is certainly not a common word anymore.
My primary reason for using that verse though is that it is just impossible to get at the meaning from the modern vantage point. I have no idea how to parse it to make it make say anything like what a modern translation says or even anything meaningful to be honest. Don't worry to do evil? Don't worry about doing evil? Don't do evil while worrying?