When I was at school, in both maths and English I was taught that double negatives make a positive: in maths, if you multiply two negative numbers, you get a positive number (I’m not sure I ever understood why) and in English, I was taught that two negatives cancel each other, resulting in a positive. ‘You ain’t seen nothing‘ means you actually have seen something.
Double negatives are sometimes used to create litotes, a deliberate understatement for effect. I think this is perhaps why the NIV translates 1 Corinthians 15:10 as God’s ‘grace to me was not without effect’), thus drawing our attention to God’s amazing and utterly effective grace. In Greek, we are told God’s grace is not in vain or empty or barren (J.B. Phillips translates this as ‘the grace He gave me has not proved a barren gift‘), but the English version does make us pause over the phrase to be clear we actually understand what Paul is saying.
Double negatives make us stop and think. Other versions put the positive spin on the phrase to make Paul’s meaning crystal clear (the Message version says ‘I’m not about to let His grace go to waste‘; the Voice version says ‘I have made sure His grace to me was not wasted.’) I quite like the linguistic effort of working through the double negative, however, to reach the conclusion that God’s grace is effective in every situation and for every person. Grace is that all-purpose ingredience vital for every day!