Thanks for drawing attention to Csikszentmihalyi's description of the "flow state." His language captures the matter nicely!
Thinking back over the course of our ongoing conversation, I think we may differ in our visions for the self. You speak of a state in which "self is gone," and you view such an end as desirable. From my perspective each "self" is a creation of God, made not to merge with God but to enjoy God and be enjoyed by God. The problem is that the "selves" tend to go rogue. That is, we focus on ourselves, enter into competition with other selves, seek power over others, and attempt to reduce or eliminate God. To put it another way, we try to take the place of God rather than the place we were created to occupy.
The ideal for the self, from my perspective, is to see, acknowledge, and willingly embrace what one was created to be. When we do so, we cease to compete with others. We start to "enjoy" ourselves, others and God. We take up work for which we are suited. To borrow a New Testament image, we come home and find it the best of all possible states in which to live.
Interestingly, though, I think both our approaches may lead to the same kind of behavior toward ourselves and others.
Turning toward the phrase "your Father who is in secret," my only point was that I do not think the biblical text in question can support the weight of your inquiry. That being said, I'm all for a round of give and take over speculative matters!
For example, the four levels of biblical interpretation you mention remind me of the multiple levels of interpretation posited by some patristic and many medieval Christian bishops and scholars. I'll not go into detail at this point, other to stress how most taught that one needed to be introduced to the perspectives and skills needed to move through the various levels. The Protestant Reformation tended to discount this approach.
Some Christian Gnostics, of course, appear to have taught that a secret knowledge necessary to fully understand the scriptures was handed down from teacher to teacher. Gnosticism was a minority movement within broader ancient Christianity, though versions of it crop up throughout history.
The latter two possibilities you suggest find parallels in Christian mysticism. In all cases (I think), a given mystic would have acknowledged that even his or her own words were but a map, not the real God found in secret.