To be? Or not to be? That is the question. I think the answer is to be as God intends. To be any other way is simply not to be. To understand who we are we need to understand God who made us in His image. So I think one of our first purposes is to grow in understanding of who God is and who we are in relation to God. Our first examples are our parents and they are meant to teach us the ways of God.
However, we were born enemies of God, and many of us lack godly instruction when we are young, so reconciliation is one of our greatest purposes, and once we have been reconciled, to stay in fellowship and to assist God in reconciling the rest of humanity to himself. God is love and we are not, so in order to be as God intended, we need to be identified with His love, demonstrated in its greatest capacity when Christ, God's son, was given for us. By placing our faith in Christ is to unlock our potential for relationship with God, and our highest purpose is then to communally and perpetually continue in this relationship forever, which accomplishes an equal purpose of bringing God glory.
In order to fellowship with God we should be overcome with a desire to obey his commands which give us life. Our lives and everyday existence at this point have "purpose" and we can "be" as God intends.