Pope Shenouda III
Thus sanctification of fasting is to consecrate it to the Lord.
Days of fasting are sacred, and are devoted to the Lord. They do not belong to the world but to the Lord’s as a sanctification to Him.
That is why God's inspiration clarified this meaning when He said “Consecrate a fast, Call a sacred assembly” (Joel 1:14,2:15), because a “sacred assembly” is fit for the consecration of the fast to the Lord, devoting it to Him.
However, what can you do if it is not possible for you to devote all your time to the Lord, and withdraw from your official work?