Colossians 2:3

The word hidden is doing something specific, and it is aimed at a particular problem in Colossae.

The teachers troubling that church were offering something extra: additional knowledge, higher insight, an inner circle. Paul's counter is not to deny that there is hidden treasure. He concedes the category entirely and then relocates it. All the treasures of wisdom and knowledge are hidden — in Christ.

So the promise of depth is not being taken away. It is being told where to dig. And the word all closes the door on supplements: if all of it is there, then anything genuinely valuable found elsewhere was already there, and anything found elsewhere that is not there is not valuable.

Hidden also implies that the treasure is not obvious. Paul is not claiming everything is on the surface. There is real searching involved, and the letter assumes a lifetime of it. What he denies is that the searching happens somewhere else.

And treasures is plural, which fits the experience. Nobody receives it as a single deposit. It comes as a series of discoveries, most of them made by people who were not looking for anything new but were reading something old again.

The verse just before this one gives Paul's reason for writing it: that their hearts may be comforted. He treats this as a pastoral matter, not an academic one.