Here are a few examples combining “that” and “which”
1-“That which” does not kill us makes us stronger.
2-Taking the time to look at “that which” has gone before, bla bla bla…
3-To do “that which” is right to do…
Could some experts please explain how to use “that which” correctly?
#1-- This famous Nietzsche expression = What(ever) does not kill us makes us stronger = Anything that does not kill us makes us stronger. = A do-not-kill-us thing makes us stronger.
#2 = Taking the time to look at what has gone before, bla bla bla…
#3 = To do what is right to do…
“that which” = anything that = the thing that = what = whatever
Maybe when we separate them, we have a better understanding:
1-That /which does not kill us/ makes us stronger.
2-Taking the time to look at that/ which has gone before, bla bla bla…
3-To do that /which is right to do…
I see no strange in this usage.