It all boils down to identity. Your soul is what makes you you. Without a soul, you are controlled by the states your brain happens to be in. Your actions are results of these states that are a product of growing up in a particular corner of this universe. So you become nothing. Your actions are not yours, they are really just part of the universe. Your identity is swallowed up and you have the flavour of an all-vanilla-universe. With a soul, however, you can now have your own identity - you are no longer vanilla... You can now play a part in your destiny, even though you are not totally free to speak Sumerian, Kalihari clicking language, Arapaho, participate in all-female mud wrestling or levitate your body.