You have more patience than I. I just give up with stuff like that, assuming the author is being flamboyant and that the line is more for show, than to actually say anything important. I mean stuff like “contradiction in reality”, and “experienced in the thing as a contradiction”, I just can’t come to terms with.
The second paragraph makes more sense to me. here he is talking about a dialectics which is “no longer compatible with Hegel”. This I assume to be negative dialectics, and he speaks of the disassembly of concretized concepts. The cognizing subject identifies them as untruth, as “the phenomenon slides in front of what is non-identical”, before the individual.
The power of that negativity rules to this day in reality. What would be different, has not yet begun.
So he continues in the next paragraph:
In the process of demythologization positivity must be negated all the way into the instrumental reason, which demythologization supplies.
In the final paragraph he speaks of an untrue whole a “summation of the totality”, and this relates back to the first sentence of the chapter:
The farewell to Hegel becomes palpable in a contradiction concerning the whole, which is not programmatically settled as a particular one.
In the following passage, I think “absolute being-for-itself” refers to that “developed summation of the totality”.
Pure identity is what is set up [Gesetzte: posited] by the subject, and to this extent is brought from outside. To immanently criticize it means therefore, paradoxically enough, to criticize it from outside as well. The subject must render compensation to the non-identical, for what it perpetrated on it. Precisely this sets it free from the appearance [Schein] of its absolute being-for-itself.