Being a part of the mouth and having much to do with formation of words, “lip” is used figuratively for speech or language (Prov. 14:3; 1 Cor. 14:21) and is occasionally used in parallelism with “tongue” (Ps. 34:13; Prov. 12:19) and with “mouth.” (Ps. 66:14; Prov. 18:7) Before the confusion of language at Babel, “all the earth continued to be of one language [literally, ‘lip’] and of one set of words.” (Gen. 11:1, 6-9; the same usage is employed at Psalm 81:5; Isaiah 19:18.) God promised through the prophet Zephaniah to give to peoples “the change to a pure language [lip],” evidently referring to the truth as revealed to his people through Jesus Christ.—Zeph. 3:9; compare Proverbs 12:19.
The lips are no sure index of what is in the heart, since they can be used by the individual to utter hypocritical speech. (Matt. 15:8) However, the lips cannot hide the true condition of the heart from God (Heb. 4:13), and they will eventually bring forth what is in the heart.—Prov. 26:23-26; Matt. 12:34.
Moses wanted to excuse himself from speaking before Pharaoh because he was “uncircumcised in lips,” that is, as though his lips had a foreskin over them and hence were too long and thick to utter speech with ease. He may have had some sort of speech impediment. (Ex. 6:12, 30) Isaiah, when called by Jehovah, wished to serve, but lamented that he was “undone” because he, a man unclean in lips, had seen Jehovah in vision, and he was unfit to carry God’s clean message. Jehovah then caused Isaiah’s lips to be cleansed.—Isa. 6:5-7; compare John 15:3; Isaiah 52:11; 2 Corinthians 6:17.
Hosea’s prophecy encouraged Israel to offer to Jehovah the “young bulls” of their lips, representing sacrifices of sincere praise. (Hos. 14:2) The Christian writer of the book of Hebrews alludes to this prophecy when he exhorts fellow believers to offer to God “a sacrifice of praise, that is, the fruit of lips which make public declaration to his name.”—Heb. 13:15.
Figuratively, “a smooth lip” denotes deceptive speech. (Ps. 12:2, 3 Such lips, as well as harsh or lying ones, can be damaging, wounding deeply like a sword or poisoning like a viper. (Ps. 59:7; 140:3; Rom. 3:13) A person “opening wide his lips” is one who speaks thoughtlessly or unwisely. (Prov. 13:3) It can bring him to ruin, for God holds everyone accountable for his words.—Deut. 23:23; Num. 30:6-8; Prov. 12:13; compare Job 2:10; Matthew 12:36, 37.