VOWS

Too often we see vows made and then broken. Sometimes the intent to keep the vow was sincere at the time, then comes the test of time.

But on the other hand, too many times vows are made without taking time to consider what you are saying or doing.

We must be careful to watch what we say, for you will be held responsible for every idle word.

Matthew 12:36
"And I tell you this, you must give an account on judgment day for every idle word you speak."

Ecclesiastes 5:4-5 
So when you make a promise to God, don't delay in following through,
for God takes no pleasure in fools.
Keep all the promises you make to Him. 

It is better to say nothing than to promise something that you don't follow through on. In such cases, your mouth is making you sin.

And don't defend yourself by telling the Temple messenger that the promise you made was a mistake. 
That would make God angry, and He might wipe out everything you have achieved.