John 4:13-14 Jesus replied, "People soon become thirsty again after drinking this water. But the water I give them takes away thirst altogether. It becomes a perpetual spring within them, giving them eternal life."
Thirst is a natural part of life. Whenever there is a lack of necessary water to sustain life, thirst comes into play. God gave every living thing a natural thirst mechanism so that sufficient water to sustain life will be provided. When there is no water for a prolonged period of time, the body shuts down and will die if water is not provided.
The same thing holds true for the soul. God gave us a natural need for Him. Every human being ever born has it. When our need for God is not provided for, we spiritually die. The reason why so many people are so bad is that their need for God was never provided for. Somewhere along the way their souls were denied the necessary food to make their soul grow or sustain it. They were not brought to the Spirit of God who fills the soul with God's presence and satisfies its longings. Or, they chose not to take advantage of the food that was provided for them and they starved their soul to death.
The only way that the thirst of the soul can ever be quenched is for the soul to turn to Christ and let Him dwell within. When Christ lives in the soul, there is such a deep and abiding satisfaction that there is no more searching, no more desperately trying to find the peace and joy every soul needs and longs for. When Christ lives in the soul, the soul is more alive than ever thought possible. Christ so energizes the soul that it he is forever changed.
Jesus satisfies every longing of the heart. Only in Christ does one find that which satisfies. The world promises a multitude of things will satisfy and make one happy, but only Christ can deliver on His promises.