Sense Holiness and Unholiness Penetration

I'm a bit confused as to how this works.

Say a demon has an Infernal Might 5 and he is hidden in the area.
Assuming Penetration 0, does that mean I have to roll 10+? 14+? 15+?

It goes on to say Divine creatures need to have their full resistance penetrated.

According to the rules on p. 184 penetration goes as follows:

So a roll of 10 on the previous example, minus the Ease Factor 9, + Penetration 0 = 1.
When compared to the demon's Infernal Might 5, it does not penetrate.
When compared to a divine creature with any might (other than 1) it does not penetrate either.

So what is the difference? :confused:

I always thought it ways saying, based on the note about them being really evil, that the Ease Factor is 1 to detect a demon. The difficulty with the demon, though, is the penetration. So my understanding is Perception + Sense Holiness and Unholiness + Aura Modifier + roll ≥ 1 + Infernal Might + Aura Modifier is needed to detect the demon.

I thought similar to Callen.
So say you have several people standing around a murdered corpse in a pentagram, and the character with Sense Holiness wants to work out what's happening.
If they can make Per + sense Holiness + aura modifier, then 9+ tells you the area is desecrated, 15+ could tell you if a given person was unholy (and therefore possibly might know who'd done the sacrificing), and 6+ will tell you if there's a might 5 demon in the area.

It makes sense, but why say Divine creatures must have their full resistance penetrated?

I'd guess that MR = MR is the best answer for that? The core book made a special stipulation that demons require only one point due to being, essentially, pure unholiness. Angels being purely divine, you probably only need to penetrate their MR by 1 as well (extrapolation, haven't found RAW in brief look.) That said, if the person with Sense Holiness and Unholiness is a good person who is working with the grace of God, the angel would probably reveal himself anyway, unless God did not desire it.

I think it's because all supernatural abilities need to penetrate to work against magic resistance, as given my Divine Might, and the penetration (p.184 of the corebook) is Effect Roll - Ease Factor + Penetration. Though the "you only need to beat it by 1 point" is quite confusing, as you actually only need to beat any magic resistance by 1 point to penetrate, with any supernatural ability (or spell), to anything with magic resistance... The description of the virtue seems to mean that with demons being so "extremely evil" you can forget about difficulty and just take their Might to beat with your Sense Holiness roll, and it makes sense because otherwise it's the same for them as for any other creature from any other realm...

In that case darkwing's numbers are true. But if there were also an angel with divine might 5 there, you would need a 21+ to discover it with your virtue (to exceed the base 15 plus magic resistance) if it were trying to hide its nature, or 15+ if it didn't care (which could be the case, if only because there it says that demons try to hide their nature, implying that other realm's being might not).