The lip as the organ of speech and also as edge/border (seashore, edge of a garment). Speech is the central meaning. 'Pure lips' signify righteous speech; the Tower of Babel divided the one saphah (language).
The lips represent the whole communicative self. Isaiah's vision (Isa 6:5-7) is resolved by a coal touching his unclean lips — speech purified for prophetic mission. Proverbs repeatedly contrasts righteous and wicked lips.
Genesis 11:1 (one language/saphah) and Acts 2 (Pentecost reversing Babel) form a bracket. The Spirit gives the church a new unity of speech — proclaiming God's mighty works in every tongue.