On the other hand, we need to know what the English words mean as well. We often assume that because we are native speakers that we just know the English side automatically. But that’s only partly true.

The trick here is that the τιμ- root covers semantic areas that are clearly distinguished in English: material worth value and price and social worth honor and rank. English is much more specific than Greek in these areas.

So ἰσότιμος could refer to someone of the same social status, someone equally worthy or to a thing of equal value. There is no clear presumption that the value is high. So, in fact, this passage could read:

“a faith that is just as good as ours”

I’m not necessarily advocating that, but precious adds a couple of factors that can’t be argued to be present in the Greek.

I have been thinking for some time now that someone needs to fill out the commercial transaction frame for Koine. I twitch at the thought. I’d love to do it, but I just don’t have the time.

Peter,
Valuable and precious are different in several ways. Precious, at least in some contexts, has an personal factor, i.e., precious to someone, but valuable is an objective evaluation. Something can be precious to someone without being particularly valuable.

One way to highlight the personal vs. objective difference, is to observe that one can easily predicate precious of a child (granted that was the way my grandmother spoke), but if you say they are valuable it has a totally different feel, emotionally remote, maybe even a little creepy. But if you are a coach, and unrelated to the child, it’s the other way around.

Grandma:
You are so precious!
Weird: You are so valuable!

Coach:
Weird: You are so precious!
You are so valuable!

In other uses precious can mean very valuable, as in precious metal.