Leftism, though secular, must be understood as a religion (which is why I have begun capitalizing it). The Leftist value system's hold on its adherents is as strong as the hold Christianity, Judaism and Islam have on their adherents.It's not new to Prager - many have proposed this theory. What's interesting about it are the implications of it.
First of all, Prager suggests fairly strongly that our Leftist religious concerns are irrational and therefore not worth dealing with. There is a gulf between world views that seems unbridgable.
But the implication is - since he clearly points to right wing Christians and Jews as being motiviated by their faith, that both sides are equally irrational? But that is presumably not Prager's intent.
He also trots out the old canard that Leftist Jews and Christians are keen on seeing Israel destroyed. Kind of sad that; a child could see that one can want to see a better situation for the Palestinians without wanting to see Israel destroyed.
At the end of the day, Prager isn't interested in understanding liberals or leftists or in helping his readers understand them. Quite the contrary; he is putting up barriers to ensure that his followers don't grapple with liberalism or leftism in any real way.