Guten Morgen, Deutschland:

This is what I get trying to construct a meaning for "Übersehbaren", but the sense doesn't seem right. Likewise, I don't see how "berechbaren" can mean "calculable" or any of the dictionary definitions here, especially when it is set opposite "Zufällige". Any help would be appreciated.

Out of the comprehensible and calculable (which, in truth, means completely incalculable) into the incomprehensible, accidental...

I would choose "comprehensible". "Overseeable" is wrong here, a "false friend".

...Aus dem Übersehbaren und Berechenbaren (d.h. dem in Wahreit ganz unBerechenbaren) in das gänzlich Unübersehbare, Zufällige...

moving from the realm of the safe and predictable (which is in fact totally unpredictable) into the completely unpredictable, random...

I suggest using safe for übersehbar, as the sense of the word, especially in the religious context, is one of "I can keep the handle on this, I can control it, foresee every eventuality". Berechenbar in diesem Zusammenhang ist das Vorhersehbare, the predicitable, what is bound to happen and happens each time.

Thank you for your input. I borrowed the English edition today. The translators (R.H. Fuller and Imgard Booth) render it as follows: "from a life which is observable and calculable (it is, in fact, quite incalculable) into a life where everything is unobservable and fortuitous." But since it is cited in a chapter entitled "Security, Goodbye!" I think the author I'm translating (Manfred Beutel) understood it more like Gismo.