Hume weakened analogical arguments for God.

[Mudhammam]

It's the part that stayed with me the most. Hume had a really novel way of framing the atheist vs theist debate that most people don't go with. His tactic could be used to undercut the cosmological arguments; atheists can say the first cause isn't the universe or multiverse but it "probably bears some remote analogy" to the universe or multiverse. Why not? The analogy is just as good as theirs. If the first cause can be like a human, then it can be like a universe or other natural processes in the universe.

A few additional comments on the Dialogues,which I rated #5 on my list of favorite books that I read in 2014. I have a much greater appreciation for it now that I'm reading the Socratic dialogues, though even when I first read Hume I knew it was a literary masterpiece. It is also one the best formulations of the antimonies and really draws out both sides of the debate on an entertaining, humorous, yet deeply philosophical level. More quotes that stuck out:

Our ideas reach no farther than our experience.

Why go so far? Why not stop at the material world?

The Brahmins assert... the world arose from an infinite spider, who spun the this whole complicated mass from his bowels, and annihilates afterwards the whole or any part of it...Why an orderly system may not be spun from the belly as well as from the brain, it will be difficult for him to give a satisfactory reason.

What peculiar privilege has this little agitation of the brain which we call ‘thought’, that we must thus make it the model of the whole universe? Our partiality in our own favor does indeed present it on all occasions, but sound philosophy ought carefully to guard against so natural an illusion.