О instead of С with instrumental case
I've come across these two sentences:

О преподобным, преподобен будешь.
О сахаром.

In both sentences I would have thought «о» would be the correct preposition. Can «о» be used as a straight replacement for «с» in colloquial language or does it also change the meaning? What's going on here?Just realised there's a typo in my question oops! It should say: "I would have thought «с» would be the correct preposition".

Question

О instead of С with instrumental case
I've come across these two sentences:

О преподобным, преподобен будешь.
О сахаром.

In both sentences I would have thought «о» would be the correct preposition. Can «о» be used as a straight replacement for «с» in colloquial language or does it also change the meaning? What's going on here?Just realised there's a typo in my question oops! It should say:  "I would have thought «с» would be the correct preposition".

Answer

Original quotation (псалом 17): С преподобным преподобен будеши, и с мужем неповинным неповинен будеши...
It's C, not O. 
будеши - is old-slavic form. Usually orthodox church books are written in Old Slavic (aka Church Slavonic), which is not quite Russian.

Answer

"О" mean "about".
"C" mean "with".
How sound sentence "(being together) About venerable, you'll venerable too"? Or "do you like tea about sugar?"

Answer

It must be a typo or just bad quality of print, if you came across it in a paper book.

Answer

Hmmm... perhaps it's just a mistake in the text then. Thank you :)

Answer

Both sentences sound wrong. "C" is the correct preposition whether it's colloquial language or not.