Augustine of Hippo

Sing therefore what follows; if you wish to hear how you may most securely set your feet on the steps, so that you may not be fatigued in that ascent, nor stumble and fall: pray in these words: "Suffer not my foot to be moved!" [Psalm 121:3]. Whereby are feet moved; whereby was the foot of him who was in Paradise moved? But first consider whereby the feet of him who was among the Angels were moved: who when his feet were moved fell, and from an Angel became a devil: for when his feet were moved he fell. …

Exposition on Psalm 121 ↗