In ancient times, and sometimes today, teachers would "sit" to "teach". This appears to have been a "private" briefing.

• "ἴδιος" ≈ "pertaining to self, one's own, private (not public)".
• "ιδιας" ≈ "own" (feminine genitive singular, feminine genitive plural)

The briefing, as remembered by Peter and related to Mark, is a "private" briefing.

• "ἴδιος" ≈ "pertaining to self, one's own, private (not public)".

From the context in Luke, based on what people remembered and told Luke some twenty years later, there is no mention of this being a "private" briefing.

Be careful not to confuse the private discourse about the end times in Matthew and Mark with the public discourse in Luke at the temple. They are much the same, but with some important differences.

Details are left as a future topic.

What are "these" "things"? They have some idea but would like additional explanation.

The Greek word for "frankness" or "openness" is often translated as "boldness". How would one define "love" "boldly" in Biblical terms?
The disciples ask: ... what is the sign of your coming. Since Jesus had said that the religious elite would not "see" "him" (Jesus) as he is until they recognized the oppressed at the bottom, the disciples would like to know when this will happen.

The ancient Greek word "σῆς" ≈ "moth" is a uncommon meaning while "σης" ≈ "thy" is a common meaning of the same word.

Could it be a "moth" coming or a "moth-ball" coming? Is it more likely that the "moth" in the "treasure" verse is that of "you"?

The Greek word translated as "world" is that of "ages" as an indefinite period of time.

• "ιωνα" ≈ "Jonah".
• "αἰῶνᾰ" ≈ "lifetime, age, forever" (accusative) of "αἰών" ≈ "lifetime, age, forever".

Jesus uses "Jonah", is in the "sign" of "Jonah", as a play on words with the "ages".

More: Matthew 12:38-40 Sign sign everywhere a sign

The discourse in Matthew 23 leads to (mistranslated) statements about the religious elite not doing what God wanted and oppressing the followers with a yoke of compulsion.

The disciples (immediately) ask some public questions (mistranslated as innocuous statements) at the beginning of Matthew 24.

Some disciples then ask private questions (mistranslated).

Jesus then follows with an extended discourse. The apparent meaning of this extended discourse, called the Olivet Discourse, is that the cooperation that should happen will never happen into the ages until the final end of time (as we know it) when heaven and earth will pass by.

What the Greek says, in context, is not at all what translations say. The translations appear to shift the wrongdoing (evil oppression) from the religious elite in general to the Jews at the time of Jesus in particular. Any group getting religious (and perhaps secular) power at a later time could point at the Jews as having a "house" that is "desolate" and could avoid suspicion as to doing exactly what Jesus said should not be done be the religious elite.

Did any group have the means, motive and opportunity to have these (and other) verses say something other than what it appears, in context, and using the original meanings of the Greek words, to have said?

The resulting English translations led, from the middle 1800's, to a date-setting and prophecy predicting movement based on the rapture, Israel, etc. Ideas on strict Biblical inerrancy date from this time. This appears to be misguided and based on questionable translations of the original Greek.

[leaven, moving mountains/definitions, etc.]