God is a perfect creator. He created everything to give Him glory. For everything He made there is a definite purpose for it . God make us in His own image that we may worship and serve Him. All the things He created,He saw it and He said that it was good. So everything that was created by God has a reason or a purpose by which it was created.As men our purpose here on earth is to serve God and worship Him in spirit and in truth. Each and every one of us have a definite assignment to fulfil here on earth, the reason by which God created us. As Christians, we are meant to follow the path of Jesus Christ who came down on earth to redeem mankind. As Jesus came down on earth, the Bible recorded that He went about doing good.
So one of the purpose of our existence here on earth is to do good, to love one another and to be our brothers keeper.
There some Christians that God gave special assignments here on earth, some are called to be a pastor ,to take care of God's people, some teachers , to reveal God's instructions and will through God's word, some evangelist, to preach the gospel to all nations etc.
No matter the different purposes that God assigned to each and every one of us, we all work together to give Him glory.