According to Bill Cooper, the 33rd degree is the point of entry to another 'pyramid within the pyramid', an elite club if you will.
IIRC, at the 32nd level, the devotee is presented with a cross and asked to spit on it...if the devotee declines, he is congratulated and told it was a test. No more promotions for him though. On the other hand, if the devotee agrees, he is also congratulated and green-lighted for the 33rd degree, the base of another, innermost hierarchy.