Suffer not thy mouth to cause thy flesh to sin; neither say thou before the angel, that it was an error: wherefore should God be angry at thy voice, and destroy the work of thine hands?
Suffer not thy mouth ... - vow not with "thy mouth" a vow (e.g., fasting), which thy flesh (thy body, margin, Ecclesiastes 2:3) may tempt thee to break (Proverbs 20:25). Ezekiel 16:26; Ezekiel 23:20 prove that "flesh" is used for carnal desires in the Old Testament as well as in the New, which Hengstenberg denies, maintaining the sense 'Suffer not thyself to be involved in guilt as respects thy whole body, by the one small member the mouth' (James 3:2; James 3:5-6).
Before the angel - the "messenger" of God (Job 33:23); minister (Revelation 1:20); i:e., the priest (Malachi 2:7), "before" whom a breach of a vow was to be confessed (Leviticus 5:4-5). We Christians, in our vows (e.g., at baptism, the Lord's supper, etc.) vow in the presence of Jesus Christ, "the angel of the covenant" (Malachi 3:1), and of ministering angels as witnesses (1 Corinthians 11:10; 1 Timothy 5:21).
That it was an error. Extenuate not any breach of them as a slight error. The distinction between sins of ignorance or heedlessness, and sinning presumptuously or willfully, is alluded to here (cf. Numbers 15:27-31; Hebrews 10:26-28).
Wherefore should God be angry? A broken vow is not to be atoned for by a few fair spoken words before a priest. Thy vow to give so much of the fruits of the earth, and of thy cattle, when not performed, will entail the destruction of the whole work of thy hands-all thy crops and cattle.