This is John's testimony, when the Jews sent priests and Levites from Jerusalem to ask him, "Who are you?"
Now, if you are not fulfilling that primary purpose of your life, then your life is bound to be empty, unfulfilling and ultimately frustrating. Because you're not fulfilling the basic purpose for which God created you. You're not answering to that basic need and necessity in man of worshipping God, fellowshipping with Him. But man did not live on this planet long before he broke that fellowship with God by disobedience, sinning against God in his disobeying of the commandment of God. And the net effect of sin is always that of severing fellowship with God. "God's hand is not short, that He cannot save; neither is his ear heavy, that He cannot hear: but your sins have separated between you and God" ( Isaiah 59:1-2 ). Sin always has that effect of separating a man from God.