Christianity is not sufficient to tell you personally the purpose of your specific life - Christian guidance is for all times and persons and situations, so guidance can be only general.
Why should it be personal? Because it is clear from the nature of ourselves and the world, and the fact that God designed it; that Men are not meant to be exactly the same or to do exactly the same.
So the exact answer differs for each of us, which (usually) means it needs to be discovered.
How, and on what basis?
How to discover the specific purpose of each of our individual lives depends upon our personal understanding of the nature of true and valid guidance: it depends on our understanding of who, or what, can and should be trusted.
My reasoning goes as follows: we inhabit the creation of a loving God, and he designed the world as a place for spiritual progression. The (extremely long term) aim or hope of this is - in brief - our divinization: that each person be given opportunity to experience, learn, develop towards godhood (the process variously termed theosis and sanctification).
And the purpose of us developing towards godhood is that we become adopted as co-heirs with Christ, fully-adult divine friends of God; so that we may live in His presence, communicate deeply and richly with Him, participate fully in His work - and so on.
Part of this ultimate and long term aim and hope is that each person is, and is intended to be, unique – because of course each divine friend would be intended to be different (no point in having identical friends), and each unique developed person would bring something different to the society of Heaven.
So; much of life is about discovering and pursuing our own uniqueness; by all good guidance possible, to the greatest extent we can manage, and inevitably by trial and error, aspiration and repentance etc.
This is possible because we have both general external guidance from God (variously available via scripture, the church, sound tradition, literature, wise persons, loving family and friends etc); and also a bit of God inside each of us – God's gift of a divine spark or a glowing coal of divinity; which works with our own distinct pre-mortal individuality as an specific evaluation/ guidance system – including pointing us at specific goals.
Locating this inner guidance system, discerning its guidance - and following it (amidst distractions and confusions produced by the environment of irrelevant and bad guidance); is therefore a vital task for those who do not already find it obvious.
Organized religions, like all human institutions, have a tendency to lapse into neglecting individuality, and to operate a cookie-cutter idea of identi-clones - equating purpose with duty, and duty with obedience to general rules.
But this is (even at best, when true, valid and necessary) both insufficient and lop-sided guidance; because the nature of purpose of life entails discovering, locating and using the inner guidance system.
And if you cannot already do it - discovery, location and usage should be made a major priority.