All Christianity concentrates on the man at the cross-roads. The vast and shallow philosophies, the huge syntheses of humbug, all talk about ages and evolution and ultimate developments. The true philosophy is concerned with the instant. Will a man take this road or that? - that is the only thing to think about, if you enjoy thinking. The aeons are easy enough to think about, any can think about them. The instant is really awful: and it is because our religion has intensely felt the instant, that it has in literature dealt much with battle and in theology much with hell. It is full of danger, like a boy's book: it is at an immortal crisis.
It uses some of Kierkegaard's favorite ideas expressed in the Kierkegaardian way: "The instant" as the true subject of philosophy, opposed to "huge syntheses" that distract a man with "talk about ages and evolution", etc. Of course, this passage isn't from Kierkegaard, but from the chapter "The Romance of Orthodoxy" from Chesterton's Orthodoxy. As far as I know, Chesterton never read Kierkegaard and perhaps never heard of him; SK did not become well-known in the English-speaking world until later in the 20th century. The fact that two such distinct thinkers, one Danish in the first half of the 19th century, the other English in the first half of the 20th, could speak with the same peculiar yet nearly synonymous voice is a reason for confidence in their message. The truth, when discovered, is what it is, whether it is discovered by a spiritually-tortured Dane, or a jolly Englishman.