One-off 'enlightenment' does Not happen (for Christians) - because of the pluralist nature of reality; and because mortal life is for learning

Anyone who has been a Christian for more than a few months will realize that our state does not bear much resemblance to the idea of 'enlightenment' which has floated vaguely into Western Culture from the East. 

By enlightenment I mean, the idea that someone attains a permanent insight, realizes the one fundamental truth about reality; and thenceforth is transformed positively and for the better ...

Or else, if there is backsliding, the path back to enlightenment consists in remembering and repeating that same original enlightenment. 

Such ideas are a part of oneness spirituality; for which there is indeed (at least potentially) a single insight of enlightenment:

Which is (approximately) that 'everything' is one - and all appearances to the contrary are maya (illusion). 

That (or, what the words point-at) is regarded as the single truth; and all possible enlightenments are of this same insight; and if one loses grasp of it, then any true future enlightenment must be a repetition of that single reality. 

But for Christians, in this mortal life, it is not like that - not even in theory. Because this life is Not one thing but many; and life is Not an illusion, but a reality from-which it is intended that we will learn. And any such learning during our mortal lives will be eternal - for all those who accept Christ's offer of resurrected and everlasting life. 

For Christians, this mortal reality is plural - not one. For Christians there ought to be many specific enlightenments. 

After all - why else would God sustain us alive unless there was more for us to learn from this life? 

When God decides that we have learned enough, or learned what we most need, then he will allow us to die; but (surely?) not until then - and of course, many leave this finite mortal life without having learned what they most need.

Therefore, in total contrast to oneness spirituality: Christian 'enlightenment' (or its equivalent) consists in many and different insights, each related to a specific need and learned from a specific context; after which we are confronted by different specific contexts from which you are intended to learn different specific lessons. 

This can lead to the dispiriting feeling of 'one step forward, one step back' - as if we are learning nothing, and there is no kind of genuine spiritual progress. 

But this is a consequence of false expectations. It is not true, or not necessarily true. A Christian who is making spiritual progress in one thing will still be confronted by the need to learn many other things.  

And any genuine spiritual 'progress' that we do make is - obviously - not primarily in terms of this mortal life; since earthly mortality is dominated by entropy (that is by decay, degeneration and death) - therefore any such progress would inevitably be temporary... 

The only durable spiritual progress is that which is 'stored' in our potentially-immortal soul and can be carried-through from this realm of inevitable loss into a realm of pure creation; where all that is Good will last forever.