I don’t think enough about how I think. Throughout the day I carry on dozens of conversations in my head and entertain a host of passing thoughts that range from dull to dangerous. Proverbs 4:23 compares the heart to the headwaters of a river or the groundwater of a spring: Keep your heart with all vigilance, for from it flow the springs of life. The proverb has always been vivid to me probably because I grew up hearing environmental lessons about how factory pollution was causing acid rain and killing our planet. So I can picture a clean, pure spring being poisoned at its source and affecting everything that flows from it. It’s a clear warning to guard your heart but leaves me unclear about how to actually do it.