Because man was entirely focused on the physical world, it monopolised his whole interest. That was a necessary stage in human development. Today, people often think: If I make an effort to live well, I will, when I die, experience what is to be experienced after death. That may seem quite logical at first, but is nonetheless entirely false, for the spiritual world will weave a veil of blindness around those who die with indifference to it, causing them to see nothing. Thinking about the transcendental world is therefore not as impractical and unworldly as it may seem.
Source (German): Rudolf Steiner – GA 266a – Aus den Inhalten der esoterischen Stunden – Stuttgart, August 16, 1908 (page 420)