Acts 18:18-28 gives us an unusual glimpse into Paul’s life, telling us that before he left Corinth and sailed for Syria, he had his hair cut off at Cenchreae because of a vow he had taken. (Acts 18:18) This was presumably something like the Nazirite vow (see Numbers 6:1-21), which involved abstinence from drinking wine and from cutting one’s hair for a period, at the end of which the hair was first cut and then burned along with other sacrifices, as a symbol of self-offering to God. Such vows were made either in thankfulness for God’s protection in the past (which Paul had definitely experienced!) or as a request for future safe-keeping.
Making vows before God was a serious business (see Deut 23:21 and Eccl 5:4-5), and in the Old Testament, we see several examples of those who made vows before God (including Samson whose parents were instructed to bring him up as a Nazirite and whose strength was bound up in his uncut hair, and Hannah, who vowed to give the son God gave her back to Him to serve Him.) Others made foolish vows (see Jephthah, whose vow to sacrifice whatever came out of his house as a burnt offering resulted in the death of his beloved daughter.) We do not fully know why Paul made a vow to God or what that vow entailed, and some have even felt it unlikely that Paul would have held fast to Jewish practices of this kind, but Paul was probably simply expressing gratitude to God and wanted to be ‘as a Jew’ to the Jews (see 1 Cor 9:20).
The Psalms remind us to fulfil our vows to God (see Ps 50:14, Ps 65:1) and Jonah says, ‘what I have vowed I will make good.’ (Jonah 2:9) Jesus talked about not making oaths or vows lightly (see Matt 5:33-38) and reminded us that we should be people of our word. Don’t make rash promises, but keep the ones you make!