He is truly within the authority of time there, so remove that pebble from your mind.

This couplet suggests that if you truly believe you are trapped by the limitations of time and worldly power, then you must first clear your mind of any lingering doubts or misconceptions. The 'pebble' in your mind represents those small, irritating thoughts or false beliefs that keep you feeling bound. To find true freedom or understanding, you need to shed these mental burdens and see beyond the transient nature of time. It's an invitation to introspection and to let go of what holds you back.