I don't know of anyone that hasn't sought the answers to, "Why do we exist? What is our purpose?'
For those that come up with the idea that we are here to serve god, I ask you now: What is god's purpose?'
If his entire existence is based on the sole purpose of creating man, He must be asking himself what he did in a previous life to deserve this job.
Whether you belief god was created, or that he has always existed, what do you think his purpose for existing is?
The Bible actually hinted a lot. Christians are told that He has an so-called Ultimate Plan, though they may not be able to tell you what this plan is.
God's primary purpose is to built an eternity called His Kingdom in Heaven. Only those you are ultimately choose to be with God are allowed to enter this realm. Those who will ultimately choose to be with sin are not allowed to enter. Because if sin is allowed to enter Heaven, then it's no longer a heaven.
He showed through Adam that those lack faith, those disobedient will not be able survive this eternity. They will finally fall as Adam did. Only those with strong faith in God and willing to obey God's Law will be able to successful live this eternity.
That's why all the covenants ever since are ultimately about Faith and Law. They are used as a measure of human faith and obedience to qualify who can enter God's realm under a well witnessed process.
On the other hand, God knows in advance that who will qualify. Planet earth is thus just a stage for this whole process to be well witnessed by both the angels and the selected humans. In this stage, everyone will finally show his true nature whether he has faith or not, whether he's obedient or not.