Why they must fast during Ramadan?

Answer 1

Fasting is stop eating,drinking, and sexual actions between married couples from dawn time to sunset to satisfy god. First fasting is a big proof how much you love god. then give the stomach (your body)a chance to rest during day hours, this is annually chance which will benifit human systems. and the last purpose to make the person feeling by the pain of the hungry people all around the world, because every Muslim should feel by his brother in faith and then by all humans.

Rasullullah Mohammad giving an example of Muslim unity is reported to have said in a Hadith:

"The Muslim Ummah is like one body. If the eye is in pain then the whole body is in pain and if the head is in pain then the whole body is in pain"

Answer 2

The general idea of fasting during Ramadan is that Muslims can experience the hunger of the poor people, a commendable thought, indeed. Well, it would be except once the sun goes down, they can stop fasting, and most stuff themselves with food before the next day's fasting.