Numbers 30:2

Two kinds of pledges are here mentioned, a vowand an obligation. A vowis a promise to give something to God. Such votive offerings were frequent in times of danger or special need (cf. Genesis 28:20-22; Judges 11:30 f.). In post-exilic times they would often consist in gifts to the temple (cf. Luke 21:5 ἀναθήματα). An obligationis a prohibition laid upon oneself, a pledge of abstinence; e.g from wine, as in the case of a Nazirite (ch. 6), or from food (1 Samuel 14:24; Acts 23:21); see also Psalms 132:3 f.

he shall not profane his word To break a solemn promise is an act of profanation. The importance of keeping vows is emphasized in Deuteronomy 23:21 ff., Ecclesiastes 5:4 f.; cf. Matthew 5:33.

all that proceedeth out of his mouth A vow is not a vow until it has been expressed in words (cf. Numbers 32:24; Judges 11:35 f.). The Rabbis of a later time further enjoined in the Mishna that the mere utterance of words without a real intention is not binding. -No utterance is binding unless the mouth and the heart agree."