In talking about his ecstatic experience, Paul says that this “man” (i.e., himself most likely) “was caught up into paradise and heard unspeakable (ἄρρητα) words that a person may (ἐξὸν) not utter.
There are two ambiguities in this verse. (1) ἄρρητος can mean “that cannot be expressed, since it is beyond human powers, inexpressible” (BDAG), or “of someth. that must not be expressed, since it is holy, not to be spoken” (BDAG). It is a NT hapax
(2) ἔξεστιν likewise can mean “to be authorized for the doing of someth., it is right, is authorized, is permitted, is proper,” or, “to be within the range of possibility, it is possible.
So was Paul unable to express what he saw, or was he not permitted to tell?