This church has extremely much light inside, compared to other churches. Not only because of the glass windows at every side, but also from above. The whole church is inspired by a forest. Huge trees (the columns) are carrying the roof of leaves and branches. Between these leaves the natural light is able to reach the ground. Here you have the same, light channels are leading light from the sky inside the church. Also a technique, Antonio Gaudi used before: in Palau de la Musica. Even the big plates with the symbols of the evangelists are illuminated from behind by natural light.
The photo above was my first photo inside, right on our way to the towers, when the inside wasn’t much crowded. On the other hand, this inner circle with the benches was guarded, to give prayers a room.