Neatly done Burke. I still see no reason at all in this case for changing the original words, but if it had to be done you've done it neatly.

I notice that you've left in the "thous", therefore, quite correctly in my opinion, ignoring the "archaic" objection. (1919 archaic? Or is the more fitting word "unfashionable"?) As my link to that other thread about "Row on" indicated, my view is that people should be very cautious about rejecting language just because it is "archaic".

The objection to "Man", though in my view it just doesn't begin to stand up in this case, is at least about something that matters.

An alternative to "Soul" might be "Friend" - "Turn back O Friend" would sound quite good, and give the song a Quakerish feeling in keeping with its message.

Both Soul and Friuend, unlike Man, direct the hymnn towards the individual rather than the human race as a whole. Maybe that is a good thing. (But I'd want to use the original.)