Allah will not call you to account for what is futile in your oaths, but He will call you to account for your deliberate oaths: for expiation, feed ten indigent persons, on a scale of the average for the food of your families; or clothe them; or give a slave his freedom. If that is beyond your means, fast for three days. That is the expiation for the oaths ye have sworn. But keep to your oaths. Thus doth Allah make clear to you His signs, that ye may be grateful.
Sometimes people do make foolish promises or oaths in anger or without foresight, such as when someone swears in anger that he will hit someone who is bothering him, or he might swear that he’ll donate a million dollars to charity when he has nowhere near that much money. God will not hold people to such foolish and futile oaths and promises. Other times people make serious promises that they have every intention of keeping but somehow fail to fulfill. To make up for breaking foolish oaths, personal penalties to pay are given here to impress upon people that a promise is important. The verse ends with an exhortation to keep rational promises and fulfill them strictly. Muslims are discouraged from making promises too freely and are especially cautioned not to swear to do something in God’s name very lightly, for our promises are our binding covenants, and God is keeping a watchful record of us.
Emerick, Yahiya. The Meaning of the Holy Qur’an in Today’s English (p. 829). Unknown. Kindle Edition.