The Quran says that Muslims should fast in the hope that one attains Taqwa (Surah Baqarah 2, Verse 183). Taqwa is translated variously as God-conciousness, piety and so forth. However, the essence of Taqwa means to abstain from the Haram (unlawful). Through fasting one abstains from food, drink and sexual intercourse with one's spouse which would normally be permissible - the connection with this and Taqwa is that it is hoped that one may develop the inner strength to abstain from the unlawful.
