Isaac seems to have figured out that MC can 'retry', based on his comment about 'next time'.
I think Isaac is playing the long game here, and has probably recognized that MC could become a very huge deal in the future - MC is likely to be a pivotal force in the upcoming rise of the demon lords. So to that end, he's powering MC up as much as possible so they can properly help each other when it's warranted and needed. (Right now, Isaac is doing most of the helping, although MC's existence has allowed Isaac the chance to interact with the world once more.)
Which brings up another point: I think Isaac feels indebted toward MC, to some extent.
There's a lot more that I could say, but this is a slim prediction of Isaac's intentions.