When someone is casting a spell using Holy Magic they cannot use Hermetic gestures or words, and therefore normally take a -15 penalty for not using gestures or words. (RoP:D p67)
However, casting without words or gestures is only an option for Formulaic and Spontaneous spells, not for Ritual spells. (ArM5 p83)
So how does a Holy Maga go about to cast a Ritual spell using Holy Magic? They can't use Hermetic words and gestures, but they cannot avoid using words and gestures for a Ritual spell.
It's explained in the next passage: "Holy magi can also learn to substitute prayer and religious ceremonies in place of their Hermetic practices, to help offset this penalty. This requires that they roll a simple die + Presence + Theology of 15+; if they succeed, they may proceed as if they had used Hermetic words and gestures, and if they fail they must continue with the –15 penalty. Alternatively, holy
characters may perform the actions associated with a Method Ability that they possess."
No that does not explain it.
It is a very difficult roll, and if they fail they get the normal penalty for casting without words or gestures - but they CAN'T cast a ritual without words and gestures.
The part about using a Method is irrelevant unless the mage actually knows a Method, which they often don't know.
Alas, it seems like these are the two ways that Holy Magi can cast Ritual spells.
Reading further, Holy Magi can cast spells using the Hermetic gestures and words, but it causes them to have to do penance, which gets more serious, and longer, the more spells they cast in this way.
Yes, that is when they use plain old Hermetic Magic - assuming they know that, and didn't learn Holy Magic from the start.
But I asked specifically about when they are using Holy Magic.
I don't cast many rituals in play, and the only time I've seen a holy mage cast a ritual it's because they had learnt Purity as a method. I suspect spending season on mysticism or pilgrimage (from The Church)to try and get Methods and Powers is the way ahead.
Alternatively you can just read books on Theology for years - eventually you'll get good enough, but it's a work of years. Yes, Holy Magic is terrible to use as a starting character unless you can get taught Methods and Powers.
Thinking on it - wouldn't having Performance Magic let a magus get around Holy Magic's restriction on no Hermetic words or gestures?
When using Performance Magic you aren't using any Hermetic words or gestures, but since you aren't casting without words and gestures you don't get the penalties for that.
Yeah that would be my go-to solution for Holy Magic.
A Holy Rusticanus could also be a solution, for the same reason.
Holy Magi can't do any Holy Magic unless they know a method, so all know at least one.
Where did you get that from? There is no requirement to know any of the holy Methods in order to have or use Holy Magic.
ErikT is right. @Plot_Device , I think you're confusing the more general Holy Magic spells with the extra guidelines that become available if you have an appropriate Method and Power. Getting access to those extra guidelines certainly requires knowing a Method, but using standard Hermetic guidelines with Holy Magic does not.
While it is three +1 virtues to make casting fully silent and with no gestures have no penalty, using those 3 +1 virtues may work.
I accept this is not an answer to the OP, and it seems, yes, Holy casters either don't do rituals, do penance or learn a method.
You're right, I didn't think about only having access to the normal hermetic guidelines. But assuming they're in a Holy Societas, they have easy access to at least one method.