what does this mean and where does it come from?

[translation]

But perhaps one can say that their grandiose failures make it easier for us who have experienced those failures to understand again the old saying that wisdom cannot be separated from moderation and hence to understand that wisdom requires unhesitating loyalty to a decent constitution and even to the cause of constitutionalism. Moderation will protect us against the twin dangers of visionary expectations from politics and unmanly contempt for politics. Thus it may again become true that all liberally educated men will be politically moderate men. It is in this way that the liberally educated may again receive a hearing even in the marketplace.


Looking for some answers from native speakers!!!

[Tdol]

I imagine it means that their ideas will be listened too in the street, by ordinary people.