Wisdom says (Proverbs 4:23) the most important thing to do in life is to guard your heart. Above all else, guard your heart, because it affects everything you do and are. The Good News Bible puts it extremely helpfully: 'Be careful how you think; your life is shaped by your thoughts'.
A person's life is not primarily made up of the circumstances which surround him. The kind of thoughts which he or she has determines the kind of world in which he or she lives. Our thoughts affect everything. Our attitudes, our goals, our values, our priorities and choices and our relationships. Marcus Aurelius, perhaps the wisest of all Roman Emperors, wrote: 'Your life is what your thoughts make of it'. Our life is shaped by our thoughts, so be very careful how and what you think'. 'As a man thinks in his heart, so is he' (Proverbs 23:7). Mind how you think.