"As a deer longs for flowing streams, so my soul longs for you, O God. My soul thirsts for God, for the living God." - Psalm 42:1-2
The deer longs for flowing streams because a flowing stream has fresh, clean water. The deer tries not to drink from stagnant water, because it is foul. Our souls long for God, because God brings the water of life.
In the Biblical world of Palestine and throughout the Middle East, life and death depended on clean water. "Thirst" is not just a desire, but a necessity for life itself.
According to The New Interpreter's Bible Commentary, "Verse 2b begins to suggest that the psalmist is exiled or at least is prevented from making a pilgrimage to the Temple to "behold the face of God." In other words, the psalmist is thirsting after God, and cannot get to the clean water.
As people of faith, we've been blessed with the gift of divine desire. When God seems distant, we notice, and long for God's intimacy to return. I feel bad for a friend who has no faith. He doesn't believe in God, but not with an atheist's fervor. He is simply "apathetic." His indifference leaves me hollow and melancholy. All passion that is not infused with the Holy Spirit, is ultimately empty.
Treat your faith with respect. God is making you thirst, and that is a gift. The thirsting calls you to the baptismal stream, where God meets you and renews your life. Do not ignore your holy thirst. It leaves you lifeless and unable to function. "Drink from the fountain of the water of life" (Rev. 21:6). When you feel the furthest from God, that very yearning is proof that God is calling you back, so you can drink in the Holy Spirit. God will never leave you thirsting for long.