Years ago, when I was learning to ski, I followed my son Josh down what appeared to be a gentle slope. With my eyes on him I failed to notice he turned down the steepest hill on the mountain, and I found myself careening down the slope, completely out of control. I cratered, of course.

Psalm 141 addresses a similar deceit by which we find ourselves slipping down sin’s slope. Prayer is one of the ways we stay alert to those slopes: “Do not let my heart be drawn to what is evil” (141:4) is a plea that echoes the Lord’s…