Once researched, it grants a defensive bonus of 250% (increase of 150%) to troops on mountain tiles, similar to Archery and Aquatism. If you have a defence bonus, a shield will appear around the health.
Meditation expands into Philosophy.
Also, it unlocks the Pacifist task, which gives you the Altar of Peace as a reward for completing it. To complete the Pacifist task, you have to make no attacks for 5 turns (Retaliation does not count as an attack).