I was reading The Secret when I came across the above quote and couldn't understand it in spite of googling
I don't know what the secret is, but the first part is probably a reference to an idea in The Lord's Prayer
...in earth, As it is in heaven...
Above is Heaven, below is Earth, and so it means
It is the same on Earth as it is in Heaven
The second is probably intended as a similar idea: within and without in this context mean inside and outside. Within is still widely used, but without is quite old fashioned.