As the Westminster Confession states it is the chief duty of man to glorify God and enjoy Him forever. This is simply enough stated. However, all men find an inability to fulfil this duty naturally because of their personal sin. God describes our dilemma as follows: "For all have sinned and fall short of the glory of God." Instead of enjoying God forever, there is a horrible fear of God that results from the conscience that knows its own guilt for sin and an innate awareness that they will one day stand before the very God they dread.
However, God through His great love wherein He has loved the world, has made it possible for sinful men and women to be reconciled to Him through the work of His Son Jesus Christ. Religion is essentially man's attempt to reach God. However, because of sin, they keep hitting a barrier that keeps men from reaching Him (cp. Isaiah 59:1-2). Christianity on the other hand, is not man's attempt to reach God, but God's attempt to reach man through His Son Christ Jesus. Only when a person has placed his/her faith in Jesus Christ and His sacrifice for sin that He provided on the cross, believing that He has been raised from the dead victorious over sin and death and therefore lives to give life to all who believe, can a person bring glory to God and enjoy Him forever.
Interestingly, once a person has been delivered from the guilt of sin, there is no longer any confusion over "what am I doing here" - they know.
I trust this helps.