You said an awful lot without actually countering it though.
"Stupid people before you believed something I think is stupid and you are stupid enough to defend it.... you are stupid"
See summarized it in one sentence for ya.
Which you appear to have not read or understood, so let me make it easier. Covenant theology is pretty simple, there are only six biblical covenants. Three have been fulfilled (Abramic, Noahic, Mosaic). The remaining ones (which continue, and are not yet completely fulfilled) are Adamic, Davidic and New. Of the remaining ones, the first addresses all mankind, second addresses the Jews, and the third also addresses all mankind.
Exactly which of them address the "Afrikaner" people exclusively in support of Buchan's statement? This is the key question, because Buchan purports to be an elder, and as an elder needs to be able to teach the truth from holy scripture.
EDIT: it's not a NGK theology, the NGK was against it at the start and only accepted it because of broederbond pressure.
EDIT: also I am not defending either him or his theology, it's not even he that was the target here he was just the patsy.
The NGK Sinod in the 70s and 80s clearly made it part their (flawed) doctrine. The "likeness to Israel" at that time (ostracisation from the rest of the world, drought, warfare) was exploited to indoctrinate the "Afrikaner" people in the belief that they were specifically shared in the covenants that God had with the Jewish people. This was the basis for Apartheid, which was justified in the light of the fact that Jewish people were prohibited to marry people of other tribes (in order to keep the bloodline clean for the saviour, Jesus Christ, in fulfillment of the Adamic, Davidic and New covenants).
Again, I have to ask you, exactly which of them address the "Afrikaner" people exclusively. What is it that you are defending, if not Buchan and his theology?