That which is within yourself - meaning

“So study these lessons as a means of awakening and training that which is within yourself”
what does “that which is within yourself” in this sentence express ?

that which is within yourself = what is within yourself = the thing which is within yourself

I did that which I ought not to have done. なすべきではなかったことをやった. There was that in her bearing which suggested an ancient race of man. 彼女の態度には古代人を思わせるものがあった. 研究社 新英和・和英中辞典

It might mean your heart, idea, soul, spirit, desire, and so on depending on the context.

I think that which to mean either that or which but with a little emphase