Parents sometimes hear their young children negotiating: “When will it be my turn?” “Just five more minutes—I promise!” Where do young children learn the technique of “promising”? Possibly from other children, but possibly from their parents. “I promise” is a modern version of the ancient practice of making a vow.

A vow in the Old Testament was a voluntary promise to God to perform a service that would be pleasing to Him in return for some desired benefit. For example, Jacob made a vow to serve God and pay Him a tithe if God delivered him safely back to his home (Genesis 28:20-22). Vows were taken seriously; there were strict protocols directing their use (Numbers 30). Solomon warned about the dangers of making a hasty vow to God: “It is better not to make a vow than to make one and not fulfill it” (Ecclesiastes 5:5, NIV). By Jesus’ day, the Pharisees had added layers of complication to vow-making which Jesus unwound. He made it simple: “But let your ‘Yes’ be ‘Yes’ and your ‘No,’ ‘No’” (Matthew 5:33-37).  

Let your word be your bond. Keeping your “Yes” or “No” eliminates the need to promise.

The life of an honest man is an oath. 
Richard Sibbes