Shabbetai Tzvi said that the Mashiach is an individual who is that last climax of the inyan of the holiness within the klipos. Therefore, in order to do his job he must go into the klipa itself, remove the oros in that klipa, and restore the last of the oros to Israel. He said it's the avoda of the Mashiach to go into the klipos consciously and voluntarily and this is a sheker ve'chazov. The inyan of the Mashiach be'soch ha'klipos is not a voluntary act. The Mashiach is born in the klipos and he can't get out of it. The Ramchal writes about this that the inyan of the Mashiach in the klipos is an involuntary inyan and it's something which causes immense suffering to the Mashiach as such, but it's not something that he G-d forbid would want to enter into. Shabbetai Tzvi felt, believed, and promoted the idea that he had to willingly go into the klipa itself in order to be clarify the last of the oros.