Spirits move through the world. The Spirit tempest uses this constant moving to attack foes and send his companions over the battlefield.
Because spirits can move very fast the Spirit tempest uses them to teleport his allies. He can also use it to spread healing of himself to others. But his abilties aren't only defensive but can also be used to attack foes. At the end of his paragon path he can combine both effect in a Spirit storm which creates a zone of damaging spirits which can also teleport the allies.