Since we rarely make oaths today, there doesn’t seem to be much to learn from Matthew 5:33-37. However, Jesus is speaking to a deeper issue than telling the truth or meaning what we say. He’s dealing with violating the 3rd commandment, taking the Lord’s name in vain.
The Vow of Jephthah
The story is tragic in part because he expected an animal, but also because his vow reveals his lack of faith in God.