only to be so

Please make the following in red clear for me.

The most venerable, clearly understood, enlightened, and reliable constant in the world is not only that we want to be happy, but that we want only to be so. Our very nature requires it of us.

Does this mean "... is not only that we want to be happy, but that we want only happiness"?

Thank you.

We don't want to be anything other than happy.

Yes - I imagine it's a fairly old text. To my ear this would sound more natural: '...not only that we want to be happy but that we only want to be that'. A current-day writer, though, might use it in a formal (perhaps academic) context.

b

Thank you all for the answer.