It simply means: (this parliament is build) for the german people. It is a dedication by the architect, he says for whom this building was made. Much like a dedication you would write on a first page of a book. http://de.wikipedia.org/wiki/Dem_deutschen_Volke It took them 21 year to finally put this revolutionary words up there, ...the emperor didn´t like them at first and was much in favour of "dem deutschen Reiche" .

Der Bundestag dient dem deutschen Volke.

Im Jahre des Herrn, Warnung vor dem Hunde, dem deutschen Reiche, nennt man "Dativ-e" , war früher normal , vor 19oo, in diesem Sinne,

Ja...warum steht drauf nicht "dem...Volk" ?

Heute würde man "dem ... Volk" schreiben.