In quantum teleportation what is the need for the extra X/Z gate after classical information is sent from Alice to Bob?

Question

In the Qiskit textbook, at step 4, Bob who has received the classical bits from Alice then needs to apply a X and/or Z gate depending on what the classical bits received are, why is that?

Answer 1

Without that fixup, the state of Bob's qubit can be in any one of the states $\alpha |0\rangle + \beta |1\rangle$ (the state we actually wanted to teleport) or $\alpha |0\rangle - \beta |1\rangle$, $\beta |0\rangle + \alpha |1\rangle$ or $\beta |0\rangle - \alpha |1\rangle$ (the states we don't want to end up with). X and Z gates are applied to fix the resulting state so that it ends up in $\alpha |0\rangle + \beta |1\rangle$ - otherwise we can't count our teleportation a a success.