Why did the chambers in Philosophers Stone let people pass?

More specifically Severus's chamber. One part of his riddle read:

One among us seven will let you move ahead,

If the whole point of guarding something, is so someone couldn't get it, why let or give someone the chance to advance, to get the object? It doesn't make sense does it? Why give someone the chance to get the object?

You may say, "So that the teachers (or Dumbledore) can retrieve it when needed."

However if the teachers made the chambers, they would create it in such a way, that only them (or any other selected people) could get past it.

OR

They would create it in such a way, that they could "hack" it, and pass the information to selected people.

Other chambers include Filius's, and Minerva's. (They flying keys, and the chessboard) These both give someone the chance to let someone pass.