The purpose of Christianity is a different thing. The OP asks our purpose. I’m not convinced that Christianity defines one. It says we should love God and neighbor, but thats not quite defining why we exist or a single purpose for us.
I will address you but others can read.
Any organization has an objective which should be briefly addressed in a Mission Statement, but we do not find the words “Mission Statement” in scripture but we do find “The Greatest Commandments” which could be our Mission Statement, briefly summarized as:
“Love God (and secondly others) with all your heart, soul, mind and energy.”
The initial objective would thus be to: “obtain this unique all consuming hugely powerful Godly type Love”, so you can Love God and others completely.
This messed up world which includes satan roaming around is not here for your pleasure, but to help you become like God Himself in that you have the unique, unbelievable Godly type Love (God himself is Love).
God has created beings to shower them with the greatest gifts possible, the greatest gift being having a Love like His.
If there is this Creator of the universe out there, His “creations” could not really “do” anything for Him, so this Creator would have to be seen as a Giver (Unselfish Lover) and not trying to “get” something from His creation.
Why would God have a totally unselfish type of Love, since He personally would not get anything out of it? If God’s “Love” is some kind of knee jerk reaction, then it is really meaningless (something like; gravity which is nice to have, but everyone automatically has it). God Loves us in spite of what we have done, who we are or what we will do, so it has to be by His choice.
God would create the right universe for the sake of the individuals that will accept His gift (the most powerful force [Love] in all universes, since that force [Love] compels even God to do all He does) and thus we become like He is (the greatest gift He could give).
What keeps the all-powerful Creator from just giving whatever He wants to his creation, eliminating the need for free will and this earthly time.
There are just something even an all-powerful Creator cannot do (there are things impossible to do), like create another Christ, since Christ has always existed, the big impossibility for us is; create humans with instinctive Godly type Love, since Godly type Love is not instinctive. Godly type love has to be the result of a free will decision by the being, to make it the person’s Love apart from God. In other words: If the Love was in a human from the human’s creation it would be a robotic type love and not a Godly type Love. Also if God “forces” this Love on a person (Kind a like a shotgun wedding) it would not be “loving” on God’s part and the love forced on the person would not be Godly type Love. This Love has to be the result of a free will moral choice with real alternatives (for humans those alternatives include the perceived pleasures of sin for a season.)
This Love is way beyond anything humans could develop, obtain, learn, earn, pay back or ever deserve, so it must be the result of a gift that is accepted or rejected (a free will choice).
This “Love” is much more than just an emotional feeling; it is God Himself (God is Love). If you see this Love you see God.
To address infant death, and how it helps some willing individuals in fulfilling their objective, you first have to realize, some individuals will never even have the opportunity to fulfill their earthly objective due to dying first. Knowing God’s Love we can imagine these individuals going to heaven without Godly type Love, but only have a wonderful child for wonderful parent type love. There will be a need to protect and preserve these individuals through eternity which those with Godly type Love would want to do, so there is a continuing need (purpose) in heaven for Christians.
Unfortunately, I, along with others, needed to see and know the brevity of life in order to respond sooner than later. Time is not on our side, since we do not get better, but worse. If everyone had at least 60 years, there would be no rush to repent and repenting does not get easier with time. We all tend to spiral down into the pigsty of life (like the prodigal son) and that does help if when we do come to our senses we turn to the Father, but that does not take 60 years.
I also want to be with my daughter and see her again, who passed away before she was one.