One is that

the “purge” is not about removing political rivals who threatened MBS’s [Mohammed bin Salman, the newly anointed Crown Prince] position as heir apparent but rather about sending a message to political and economic elites that their entitlement to extreme wealth and privilege, and their impunity, is coming to an end.

Indeed,

With the exception of Minister of the National Guard Prince Mutaib bin Abdallah, the detainee list is made up entirely of individuals who had no capacity to challenge the succession.

The other view is that

Despite his youth and inexperience, he [MBS] has risen rapidly through the ranks, amassing previously unimaginable powers for a single royal. This, and his refusal to govern through consensus—as is customary—has caused deep resentment, jealousy and anger. His most prominent critics and rivals were therefore carted off on corruption charges.

So, maybe a purge after all—but of whom?  Apparently not threats to his political power:

[T]he wider significance of this can only be fully understood in conjunction with events in Israel. The Jewish state is hardly a natural ally for Saudi Arabia, but they have long shared a common enemy: Iran.
…
So the two have been working together: close diplomatic cooperation, intelligence sharing and perhaps more.

And the possibility of an actual alliance may be growing.  The purge, thus, could be a clearing of the decks in anticipation of an Iranian-backed anti-Saudi Arabia program (expanding its Yemen program—recall the Houthi launch of an Iranian-supplied IRBM against Riyadh—supporting another client’s efforts against Saudi Arabia, …) if not an overtly fought military action.

Nor are the two views mutually exclusive, and they could be entirely independent of each other.  Overt dispute with Iran or not, the Saudi economy in the post oil-only economy can prosper only with corruption in government and other high places eliminated or at least greatly reduced.  On the other hand, Iran seems intent on taking over the Middle East, and that has negative implications for both Israel and Saudi Arabia.  With Iran’s view of how to run things, too, the implications would seem to be no less catastrophic for the Saudis, regardless of the degree of corruption.