“Blessed are those who hunger and thirst after righteousness, for they will be filled.”
The mind is avaricious and wants to feed itself with knowledge and opinions about that knowledge. Jesus is saying, “Be ready to do a lot of fasting. You’re not here to fill your stomachs, or your minds. If your motive is for anything other than to partake of the truth, you’re in the wrong place. You are here to become God-realized, not to acquire a new philosophy or to live comfortably.”
Jesus is also telling his students that they will be doing a lot of literal fasting. Fasting has always been a regular part of spiritual training. There is a notion, more among lay people than spiritual aspirants, that life in the monastery is plush, or at least sheltered with “three squares a day.” Jesus is laying this to rest at the outset.
Even though there is no mention in the Bible of a monastic lifestyle amongst Jesus’ disciples, they undoubtedly lived communally or in small groups. While Jesus and his entourage toured the countryside, there must have been a substantial number of people staying at home taking care of business. The economics of daily living was the same then as it is now, and Jesus’ activity must have required much planning and support.