Elizabeth Yates wrote of Sir Gibbie, "It moved me the way books did when, as a child, the great gates of literature began to open and first encounters with noble thoughts and utterances were unspeakably thrilling."
Even Mark Twain, who initially disliked MacDonald, became friends with him, and there is some evidence that Twain was influenced by MacDonald. Christian author Oswald Chambers (1874–1917) wrote in Christian Disciplines, vol. 1, (pub. 1934) that "it is a striking indication of the trend and shallowness of the modern reading public that George MacDonald's books have been so neglected".
In addition to his fairy tales, MacDonald wrote several works on Christian apologetics including several that defended his view of Christian Universalism.