You must devote three things: your heart

[Mary Naeem]

Pope Shenouda III

You must devote three things: your heart, thoughts, and will in order to consecrate you fast to God.
You should not be overly occupied with food and drink. Rather, your abstention trains you to have a strong will over what you eat and drink. When you succeed in controlling what you eat, your will submits itself to God in all things and your desires will be nothing but what God wants.
This is the wisdom behind fasting. Controlling our desire for food extends itself to controlling our conduct, which displeases God. It is not sufficient to abstain from or eat vegetarian food while at the same time unable to control certain sins! You should strive to submit your will to God in all that you do, saying to Him, "Let it not be my will but yours."