'A lip' in general signifies doctrine.

In Isaiah 6:3, 7, this signifies the interior parts of a person and thus internal worship where adoration is grounded.

In Isaiah 37:29, this signifies the thought of the understanding

In Malachi 2:6, 7, this denotes doctrine grounded in charity.

(Referencias: Arcana Coelestia 1284, Arcana Coelestia 1288)

1284. Verse 1 And the whole earth was of one lip, and its words were one.

'The whole earth was of one lip' means that people everywhere held to the same doctrine in its general aspects, 'lip' meaning doctrine, 'the earth' the Church. 'And its words were one' means that they held to the same doctrine in its particular details.