The term "national idea" is an unclear one. One might think of it as a widely shared understanding among a people as to the desired way of life in their country, an idea that holds sway over the population. A unifying concept like that can be useful, but should never be created artificially or imposed top-down by the powers-that-be.
Aleksandr Solzhenitsyn[He] understood the people in a new way...The people is not everyone who speaks our language, nor yet the elect marked by the fiery stamp of genius. Not by birth, not by the work of one's hands, not by the wings of education is one elected into the people. But by one's inner self. Everyone forges his inner self year after year. One must try to temper, to cut, to polish one's soul so as to become a human being. And thereby become a tiny particle of one's own people.
Aleksandr Solzhenitsyn