Where did I come from? When did I come into existence? Why am I here?
According to religion, we all came indirectly from God. God created the first man and woman. They then became the progenitors of all humans. After Adam and Eve, each of us came into existence when our parents decided to procreate us. Our individual existences are all the result of sexual procreation, either deliberate or accidental. Prior to conception we did not exist at all.
The religious answer to question three is supposedly that we are here to please God, by first figuring out what it takes to please Him and then to actually perform the necessary pleasing steps. The result of His pleasure is eternal life, a home in God's presence, and eternal bliss. By implication mankind was created so God could experience pleasure by observing man's obedience and subservience to Him.
Most all shades of Christianity adhere to the idea that God abides and operates in a spiritual realm, removed from the physical that we humans experience daily through the senses. Humans live and operate in the physical realm, and it is there that they fall prey to sinfulness which then bars them from acceptance by God in the spiritual realm. The basic problem goes all the way back to Adam, when an improper physical action drove a wedge between God in the spiritual realm and man in the physical. By implication the operation in the physical impacts God and the other realm.
Per religion, what it took to correct a problem in the spiritual realm was a series of prescribed activities in the physical. Certain events in the course of human history were orchestrated by God in order to correct, partially or wholly, the sin problem which originated on earth but which ultimately has its greatest impact in a spiritual eternity. Physical events correct a spiritual problem.
The real question is what is the connection between the physical existence we enjoy here and now and any other form of existence we may experience. Why do we enter the physical on the road to the spiritual? Much religious thought suggests that we are here to prove ourselves, to earn a place in the spiritual hereafter. Some, though, think we are here to grow through the human experience, to develop in awareness. Of course, others think that there is no reason we are here other than blind chance.
Those familiar with concepts apart from those of Christian Orthodoxy know that, outside our society, many embrace the idea of reincarnation, a process of serial lives in which men gradually grow in awareness till they meet their full potential. Others believe that we have always existed and have no beginning or end, no different perhaps than God. Under this paradigm, human life becomes a time of forgetting eternity past while preparing in some way for eternity future.
Personally I find it more and more difficult to accept that historical events on earth somehow altered God's attitude toward anyone, allowing Him to accept a select few. If God is transformed by anything in human history, I believe it must be by the totality of human experience, in all its frailty and messiness. Maybe that divine transformation is the underlying reason we are here, perhaps along with our own need to develop.