Jeremiah 17:1

¹ The sin of Judah is written with a pen of iron, With the point of a diamond, Graven on the tablet of their heart, And on the horns of your altars,

Lip

'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.