Ramadan is the month in which Muslims observe the obligatory fast which has been prescribed by God on those who believe in Him as it was prescribed on previous nations.
O you who believe! Fasting is prescribed for you, even as it was prescribed for those before you, that you may attain piety. (Al-Baqarah 2: 183)
The above verse explains the main purpose of fasting. It is to attain taqwa (God-consciousness) which means that every Muslim must be watchful of everything. He must watch out every word he utters and every action he does.