Paging All Greek Scholars

Gather ‘round nerds, I need your wisdom.

In Matthew 5, Jesus blesses the poor in spirit and says the kingdom of heaven is theirs.  I’ve studied this verse and the ones right after it for more than three years now and last night I ran across something new.  The thing is I’m not sure I believe it because it’s something I’ve only found in one book out of five dozen I’ve read on these verses.  Makes me wonder how legit the insight is.  So, if you know Greek and can back up or deny this info or tell me where to go for that I’d appreciate it.  Here’s the new insight:

A guy claims that “For theirs is the kingdom of heaven” is a bad translation of the Greek original.  He says it is more accurate to say “for from them” or “for through them.” As in “for through them comes the kingdom of heaven.”

He says…This is the partitive genitive idea.  The possessive genitive is more widely used – “for theirs is.” But the poor in spirit do not own the kingdom of heaven.  They make up the kingdom of heaven.

I’m curious if there’s anything to this.  Do you know?  Thanks for your input.