lit. to sharpen one's sword (idiom) / fig. to prepare to attack / to be getting ready for battle
磨刀不误砍柴工
mó dāo bù wù kǎn chái gōng
lit. sharpening the axe won't make the wood-splitting take longer (idiom) / fig. time invested in preparations is not lost / a beard well lathered is half shaved