It is just as one begins to discover the spiritual world, that he becomes aware of how little he actually knows about it. We have no reason to fear those with deep spiritual knowledge becoming arrogant. Pride may only overcome those who speak in phrases about the spiritual world, who talk about the spirit without having any knowledge of it, and refer to it in purely philosophical terms. But those who penetrate into the spiritual world, become certain that neither arrogance nor stubbornness will ever touch them, because they realise how insignificant they are compared to that world.
Source (German): Rudolf Steiner – GA 329 – Die Befreiung des Menschenwesens als Grundlage für eine soziale Neugestaltung – Bern, 6 November 1919 (page 278-279)