That the same standard by which you judge and by which you forgive will be applied to you.
This same thought is repeated throughout the new testament.
It is a command to put your own house in order.
I think the “measure” refers to charity and generosity; and not to condemning someone to hell.
The latter is not quantifiable. The former, is.
Oh, and all these verses were imagined and written down by men, by the way.