I have surveyed more than 10 commentaries on this, some comment on these verses specifically, and the ones that do disagree somewhat. It is not clear to me if the meaning of these words is clear, or if they are somewhat ambiguous. Also are they connected?
And He was saying to them, “Take care what you listen to. By your standard of measure it will be measured to you; and more will be given you besides.
“For whoever has, to him more shall be given; and whoever does not have, even what he has shall be taken away from him.”
Perhaps Jesus is referring to the Jews and their guardianship of the Law, or their added law, i.e. it is a negative statement. Perhaps Jesus is referring to gifting/knowledge/understanding, i.e. its a positive statement, for those who handle their talents well.
If verse 24 is a reference to Jews, then verse 25 is a bit more problematic, perhaps, those without the law have its requirements taken away? If verse 24 is a reference to handling gifts, then 25 is completely straightforward.
Interestingly, NLT applies some interpretive gloss, showing an interpretation that has not occurred to me before:
Then he added, “Pay close attention to what you hear. The closer you listen, the more understanding you will be given—and you will receive even more. To those who listen to my teaching, more understanding will be given. But for those who are not listening, even what little understanding they have will be taken away from them.”