It is almost literally impossible to describe — using human language — the interior of Sagrada Familia. It is unlike any other church you have ever experienced because its architecture is alien to all other forms to which you are accustomed. Where you expect straight lines there are curves. Where you expect curves there are angles. Where you expect colors there there is monochrome. Where you expect blank space there is text. Nothing is what you expect. Nothing is where you expect it, yet all of it 'works' to evoke wonder and awe and religiously-tinged emotional reactions.
You wander through the space unable to fully grasp what you are seeing, and leave wondering what it was you just experienced, yet absolutely certain that whatever it was will stay with you for a very very long time.