Magic level is good for healing, hiting and to use runes.
Magic level for knights is good for healing, because when he use would cleansing it heals more. For damage knights don't need magic level soo much.
Paladins need magic level to heal, because the magic level don't changes very much the damage.
Mages need a high magic level, because all their attacks use magic, so the higher magic level, higher the damage.
So all vocations need magic level.