Hunger is caused by a need for food. Thirst is caused by a need for something to drink. Hungering and thirsting, in this situation, are the recognition of a spiritual need for righteousness. The main thing that would keep us from experiencing this hunger and thirst would be because we were already filled with something else. Usually that “something else” is a concern for the opinions of people or for having physical things.

Mat 6:31-33 (NIV) So do not worry, saying, ‘What shall we eat?’ or ‘What shall we drink?’ or ‘What shall we wear?’ For the pagans run after all these things, and your heavenly Father knows that you need them. But seek first His kingdom and His righteousness, and all these THINGS will be given to you as well.

We feel the desire to make sure we have all the physical needs of life met. This Scripture tells us how to get them through God as our source. As we concentrate on an intense passion for God and His righteousness, He takes care of us and our physical needs. If we concentrate on the things of the physical as our first priority, they will crowd out the issues of God’s Kingdom and His righteousness. It is all dependent on what we seek first.