Asking about a time before the beginning of our spherical spacetime is like asking what lies north of the North Pole. There is no such thing.

To talk intelligibly about modern physics, we have to admit the possibility of uncaused events.

Of course, Jastrow's comment is exaggerated at best; theologians hardly predicted the Big Bang. If our universe turns out to be closed, hence with an end, this does not mean apocalyptic visions of the end of the world were on target. And even if a beginning for the universe is a successful prediction of one version of theism, this is still not that impressive. After all, even a stopped clock is right twice a day. The Big Bang becomes strong support for God only with an argument showing that such a beginning requires a Creator.

Creation out of absolute nothing is a metaphysical quagmire for theists anyway, since nothing must at least have the potentiality for becoming something. Since theists are stuck with potentiality, it might as well be something like a quantum vacuum.

In the popular imagination, the Big Bang is a great explosion; at one time there was nothing, then matter erupted into previously empty space. However, the Big Bang is the beginning of spacetime itself, not an event in time.

Which is better: to achieve Nirvana, or become a Boddhissatva?

Asking about a time before the beginning of our spherical spacetime is like asking what lies north of the North Pole. There is no such thing.