This excerpt is from Maximus the Confessor, Ad Thalassium 60: On the Cosmic Mystery of Jesus Christ (CCSG 22:73-81). It is a minor paraphrase (for readability only) of the translation by Paul Blowers and Robert Wilken (St. Vlad's Press, 2003).
Scripture teaches us two ways of knowing God, two kinds of knowledge of divine things.
First, there is what we might call 'relative knowledge,' which is rooted in human reason, ideas and conceptions. Relative knowledge lacks the kind of direct, experiential perception that we get by active engagement or a living encounter. This relative knowledge is what we typically use to order our affairs in our present daily lives.
On the other hand, there is a second kind of knowledge--a truly authentic knowledge--gained only by actual experience, apart from and beyond human reason and ideas. This authentic, experiential knowledge gives us a direct perception of God through participation in his life by grace.
We will ultimately attain this second way of knowing in the next life by participation in God's nature ('theosis'), as he transforms us from glory to glory into the image of Christ. This will be a supernatural and unceasing process.
Scripture shows us how the relative knowledge based on reason and ideas can be a useful motivator, increasing our desire for the participative knowledge acquired by active engagement.
Further, they teach us that this active, experiential knowledge through participation, which gives us direct perception of God, can supplant (replace, displace) the relative knowledge based in reason and ideas.
The great sages go so far as to say that it's impossible for rational knowledge of God coexist with the direct experience of God. Or for human conceptions of God to coexist with the immediate perception of God.
'Rational knowledge of God' uses analogies from created beings in the intellectual contemplation of God. Similarly, 'conceptual knowledge' means all the simple knowledge of God drawn from created beings. But 'immediate perception' involves actual experience, through participation, in the supernatural life of God.
We use this kind of distinction with every other kind of knowledge as well, since our direct experience of something suspends our rational knowledge about it. And our direct perception of things makes our conceptual knowledge useless. This kind of 'experiential knowledge' refers to is based in firsthand, active engagement, which surpasses all reason.
So when we speak of 'immediate perception,' we are referring to our participation in whatever (or whomever) manifests itself to us beyond all our human-based analogies and conceptions.
This may very well be what the Apostle Paul is secretly teaching when he says, 'As for prophecies, they will pass away; as for tongues, they will cease; as for knowledge, it will disappear (1 Cor. 13:8). Clearly he is referring here to that knowledge which is found in reason and ideas, which disappears in light of the direct experience of intimate encounter.