Whoever fasts a day in the way of Allah, Allah will keep his face away from the Fire seventy falls

An-Nawawi said: The merit of fasting in the way of Allah, and it is meant to apply to whoever is not harmed by it, does not neglect any rights because of it, and does not hamper his ability to fight or fulfill any of the missions of his fight.
Encouraging and motivating the voluntary fast.
It is obligatory to offer the fast sincerely for Allah's sake and seek His pleasure, not for showing off, gaining a good reputation, or any other purpose.
As-Sindi said: His statement (in the way of Allah) may mean simply having a sincere intention or fasting while being a warrior in battle. The second meaning is the more apparent one.
Ibn Hajar said: His statement (seventy falls) refers to fall as a specific time of the year, but here it means a year. Fall is mentioned specifically instead of the other seasons—summer, winter, and spring—because fall is the most fruitful season, as it is the time when fruits are harvested.