If you listen to ‘The Devil Went Down to Georgia’ by the Charlie Daniel’s Band there’s a line that reads:
Johnny, rosin up your bow and play your fiddle hard
After years of listening to this I’d always wondered by ‘rosin up your bow’ meant.
The word rosin is the key part to the phrase, and rosin refers to a substance used to treat the bows of stringed instruments (including a fiddle as heard in the tune). Rosin itself is the solid amber residue that remains after turpentine oleoresin or naptha from pine trees is destilled. Rosin is not just used for bow strings, it’s also used in adhesives, varnishes, inks and, in powdered form, as an anti-slip agent (similar to the use of chalk in weightlifting or gymnastics).
Wikipedia has an excellent page that goes into more detail.