That wasn't heaven calling; that was Rick having a breakdown. He made it pretty clear that he felt guilty about the people he couldn't save, the people he'd had to kill, what his son was going through. I thought that was all fairly obvious. He needed to be forgiven, so he invented this conversation in his psychotic break.
Yes, thank you, We/I get that, just playing what if here, what if the writers are in fact messing with our minds?