A vow is a pledge to keep our word, literally our honor. Once a Christian makes a vow, it's a binding contract, and must be fulfilled regardless of the cost. You can make a unilateral vow, which means you promise to do something, regardless of what the other party does. Or you can make a bilateral vow in which you promise to do something if the other person does his or her part. You need to be sure that you understand exactly what the guidelines are in any contract you agree to.
Vows seem to be conditional today.
Many people feel that a contract made under one set of circumstances can be broken if the circumstances change. In past generations, vows were a commitment of honor. When an honorable person shook hands, it was a deal. Even if it required all he or she owned, an honest person would fulfill the vow. The outside indicator of an honorable person is a good name.