What does “unsearchable” mean in “the unsearchable riches of Christ”. Ephesians 3:8?

Ephesians 3:8

"To me, though I am the very least of all the saints, this grace was given, to preach to the Gentiles the unsearchable riches of Christ,". ESV. My emphasis. [unsearchable/anexichniaston].

1. Are these riches of Christ "unsearchable" to all people or just some?

2. Are all "riches of Christ" unsearchable or just some of them?

3. Can these riches of Christ ever be described, discovered, understood or experienced?
   If riches of Christ can be understood in what way are they unsearchable?