A vow is to promise. It was not imposed as an obligation. The Lord never said to vow, but if you should make a vow, then let the conditions of it be observed. A broken vow puts a slight on God and a stain on the worshipper. 

What about your vow? Give me one more chance. Deliver me from myself. Save my husband. Give me a praying wife. Protect my children. Heal my body. Bring me through this operation. Remove the taste of alcohol. Be with me in the courthouse. Get me out of this prison. Provide me with a job. Do this and I promise to...  Can you hear me, Lord?