Is Existence Weakness?

Spinoza writes, "To be able to not exist is weakness; on the other hand, to be able to exist is power, as is self-evident." I am not sure that this is actually self-evident. If one looks at God from the perspective that He does not exist one could still argue that God is very powerful for wars have been waged and societies shaken by Him regardless of whether or not he actually exists.

Additionally, if something is infinite- how can we know it? For do we not know things by our ability to distinguish them from one another? Could I know white if it weren't for black? I say that if God exists there would have to be an absence of Him in order for us to be able to know Him.