Since Christianity is simple, it is existential.

Luke 18:
15And they brought unto him also infants, that he would touch them: but when his disciples saw it, they rebuked them.
16But Jesus called them unto him, and said, Suffer little children to come unto me, and forbid them not: for of such is the kingdom of God.
17Verily I say unto you, Whosoever shall not receive the kingdom of God as a little child shall in no wise enter therein.

Since Christianity is simple, it is existential.

This statement claims that Christianity is simple due to it being existential by nature. Christianity is not found in reason, the intellectual, the doctrinal, or the systematic. Christianity is essentially existential, and one virtue of an existential Christianity is that it is simple (simple in the sense that its essence is entirely independent of intellectual complication).

This does not mean a Christianity that is anti-intellectual or definitively irrational, however, since it does not necessarily follow that being independent of reason means being in conflict with reason. What I am trying to get at here is that the essence of a simple Christianity lies in our existence within the world, not our intellectual contemplation within the mind.

Existential Christianity is not just about privileging the practical over the theoretical though. Existentialism is not about ignoring the ultimate intellectual questions (such as “what is truth?”, “what is real?”, “what is the meaning of life?”), but rather finding the answers to these questions within our lived experience and not reason. Philosophers (such as the existentialists) come to this conclusion through their philosophy, poets through their artistic musings, workers through their work, and lovers through their love.

In conclusion, Christianity is simple and Existential. Those two terms are interconnected, but not entirely synonymous. Modern Christianity is not essentially existential, and thereby it is not a simple Christianity. It is caught up in the rigours of the doctrinal, to the point where it is now claimed that Christianity is these doctrines, and are constituted by them. Jesus wants followers to come to the kingdom of God as a little child, and by that he is pointing out the virtue of existential innocence that little children possess.