“’When a man begins to fast, he straightaway yearns in his mind to enter into converse with God.’ (St. Isaac the Syrian, Homilies 37, in Ascetical Homilies, p 171)
‘Fasting was the commandment that was given to our nature in the beginning to protect it with respect to the tasting of food, and in this point the progenitor of our substance fell. There, however, where the first defeat was suffered, the ascetic strugglers make their beginning in the fear of God as they start to keep his laws. And the Savior also, when he manifested himself to the world in the Jordan, began at this point. For after his baptism the Spirit led him into the wilderness and he fasted for forty days and forty nights. Likewise all who set to follow in his footsteps make the beginning of their struggle upon this foundation. For this is a weapon forged by God, and who shall escape blame if he neglects it? And if the Lawgiver himself fasts, who among those who keep the law has no need of fasting?’ (St. Isaac the Syrian, Homilies 37, in Ascetical Homilies, p 172)

‘What weapon is more powerful and gives more boldness to the heart in the time of battle against the spirits of wickedness, than hunger endured for Christ’s sake?…He who has armed himself with the weapon of fasting is afire with zeal at all time.’ (St. Isaach the Syrian, Homilies 37, in Ascetical Homilies, p 172)”
(Matthew the Poor, Orthodox Prayer Life, p 231)