By believing in immortality through rebirth: the everlasting chance to learn, make mistakes, and try different things, has helped me transcend that.?

Immortality through reincarnation is equal to the Christian notion of eternal life after death. Both involve an idea of a soul that lives separate from the physical body. It also alleviates responsibility from your immediate circumstances, as you hold hopes or dreams for another chance, another life.

Satanism rejects that notion.

Magister Svengali best described the notion of a "soul" as what people commonly use to refer to their mental/emotional lives.

Therefore it enters into common usage and has a certain legitimacy in popular thought.

(some people simply believe in a nothingness that ensues death - while this serves their purpose, it makes life seem empty and pointless to me - what, if there is nothing, are we trying to achieve then?

On the contrary, it makes my life seem fuller. By rejecting the notion of any life after death I am starkly reminded that my focus needs to be on THIS life, here and now. By focusing on an ephemeral notion of a "soul" you allow your life to be pointless.

And of course there's that whole, "Life after death through fulfillment of the ego" thing.