Consider 神のご加護があらんことを

1. How is あらんことを different from あろうことを ?
   (c.f. archaic -an conjugation)
   Apart from sounding archaic, are there other functional differences?

2. How is {あらん・あろう}ことを different from あることを ?
   What does the volitional form do that the plain form does not in this phrase?

Is there a preference for one of the forms? I.e. is there an idiomatically frozen choice that is chosen over the others.

3. How idiomatic is ～ことを ? Is it such that we do not even consider if there is any possible verb that follows after it? If there is an implicit verb, would it be something like お願いします or 祈ります ?

Consider 神のご加護があらんことを

1. How is あらんことを different from あろうことを ?
   (c.f. archaic -an conjugation)
   Apart from sounding archaic, are there other functional differences?

2. How is {あらん・あろう}ことを different from あることを ?
   What does the volitional form do that the plain form does not in this phrase?

Is there a preference for one of the forms? I.e. is there an idiomatically frozen choice that is chosen over the others.

3. How idiomatic is ～ことを ? Is it such that we do not even consider if there is any possible verb that follows after it? If there is an implicit verb, would it be something like お願いします or 祈ります ?