Deuteronomy 23:22

But if thou shalt forbear to vow, it shall be no sin in thee.

Making a vow to God is voluntary and not required, so to refrain from vowing is no sin and brings no guilt. Freedom lies in whether to vow at all, while duty begins once a vow has been freely made. What a person has vowed must then be kept and paid as promised. The obligation to fulfill applies only to what was actually vowed, not to any vow never made.