One might consider the "understanding" of Jesus' parables, to be hidden manna. Another, might consider that "understanding", to be having the "key of David." whereas, yet another, might look at it, as Israel did in Moses' day, of trudging through the wilderness, and say: "What is THAT?" Which is the translation from the Hebrew for "manna."
Which means that, any one, or all of us, at one time or another, may have been given hidden manna. But, instead of partaking it? Ya said: "What's THAT?"
Hidden manna is the spiritual understanding (food) found in parables hid from the lost.
Great point .Define the word to start with a proper meaning. (What is it? ... not when as to a time factor)
After a great display of God power moving a nation set aside for the special purposes of God. Men stared complaining and familiarity crept in. It as it was designed starting breeding contempt and hatred the natural cause of familiarity.
In the case of the Son of man . he came to his own and they received Him not. This was a false zeal for God familiarity had provided its work Just as Christ beforehand said it would. (They rejected me without cause.)
You could say the Jew had become familiar with the signs and wonders that were directed at the unbelievers. Signs are for those who rebel. Prophecy for those who walk by faith the unseen understanding.
The outward unconverted Jew that did not have the Spirit of Christ in them had expected to see ta sign before they world believe, It made them murmur against Moses just as it did against the Son of man.
The Jews in that way still seek after a sign, requiring them before they will believe. They always insisted that the Son of man perform a sign like a circus seal. Christ called them an evil generation (natural man) that does walk by sight... and promised them no sign would be given.
Parables today still hide the same spiritual truths ( What is it?) to those where familiarity has come in because of a false zeal of knowing God. .
I think it could be considered lukewarmness .When men start to take things for granted and therefore give up on working to maintain a relationship relationships can die..
Rather than spue the people out of His mouth this time he had mercy on them he fed them the spiritual food .The same kind of food disciples knew not of when Christ hid the meaning from them.
So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth.Because thou sayest, I am rich, and increased with goods, and have need of nothing; and knowest not that thou art wretched, and miserable, and poor, and blind, and naked:I counsel thee to buy of me gold tried in the fire, that thou mayest be rich; and white raiment, that thou mayest be clothed, and that the shame of thy nakedness do not appear; and anoint thine eyes with eyesalve, that thou mayest see. Rev 3:18
The gold tried by fire I think would be the spiritual understanding he does give us. Gold represents the hot or cold believer.
Not the lukewarm that requires a sign