Luke 12:25

“And which of you by being anxious can add a cubit to the measure of his life?”

The word used here may mean ‘to his measure of life', for while ‘cubit' may seem to suggest the length of an object, outside sources do in fact speak of a ‘cubit of time'; and we can compare with this Psalms 39:5 where ‘a handbreadth' is used to describe the length of days. Or the same word may mean ‘to his stature.' The former would fit in with the last parable when death came suddenly (compare Psalms 39:4). The idea is then that men cannot extend their lives by ‘even the smallest amount'. How wise then not to have spent their time in sowing and reaping and building barns when they cannot extend their lives even by a fraction (so also Luke 12:26). It also fits in with the thought that those who followed Him might be martyred, with the idea that the times are in His hands, so that trying to extend their lives is a waste of time. ‘Add -- to his stature' would tie in with the flowers growing in Luke 12:27, but we should note that the growing is not the important point there. The growing is incidental to the main point. And who in general would normally want to add eighteen inches to their height? (And besides it would hardly be called ‘the least' in Luke 12:26). Thus we would favour the former.

Nowadays we might feel that we can extend our lives by wise eating. And all things being equal we should do so. But not to the extent that it gets in the way of our dedication to God.