[19a bottom] Braisa: A glass vessel may only be purified by rendering it unusable; ie: by making a HOLE in it. It may then be filled with glass to be classified a “new” usable holder. [A metal plug would not work because it has a unique Halacha of reverting back to an impure status.]
E’s Lesson: To absolutely fix something, many times a destructive process is required. A “Teshuva” (returning to proper state) necessitates becoming HOLE-Y (in BOTH senses of the word). First, we must pierce our shells to let stubbornness and selfishness ‘leak out’ through the holes we create. Secondly, when we re-plug, we must fill ourselves with holy selfless mindsets and purely altruistic actions.