undone - (Exo 33:20). The same effect was produced on others by the presence of God (Jdg 6:22; Jdg 13:22; Job 42:5, Job 42:6; Luk 5:8; Rev 1:17).
lips - appropriate to the context which describes the praises of the lips, sung in alternate responses (Exo 15:20, Exo 15:21; Isa 6:3) by the seraphim: also appropriate to the office of speaking as the prophet of God, about to be committed to Isaiah (Isa 6:9).
seen - not strictly Jehovah Himself (Joh 1:18; 1Ti 6:16), but the symbol of His presence.