There is a new Sage Advice about the rules of spellcasting by Jeremy Crawford.
I think it's funny that he answered how much interaction a focus requires but didn't talk about how this relates to two-handed weapons only versatile weapons. I guess it doesn't really matter, as I will continue to allow it, but it would have been interesting to get their perspective.
No surprises.
Though the one odd thing is that while you can cast a M,S spell with a focus, you cannot cast just an S spell.
Somehow having more requirements makes it easier to cast.
My preference...
V = breaks stealth, can be silenced.
S = needs a free hand / focus
M = requires an items / focus
It is true that if you have a hand free to satisfy having access to your material components, that hand can also be used to satisfy somatic components (based on the text under 'Material (M)' in the PH, Basic Rules).
The Sage seems to be implying that if your hand is holding a material component (such as a shield with a holy symbol or a wand) then that hand can also be used to satisfy somatic components even though the hand is not technically 'free'. This makes more sense for a wand than for a shield, but based on the wording of how a holy symbol can be used, the official answer is defensible -- if you can trace somatic gestures with a wand in your hand but not with a shield in your hand, why is that different?
This ruling interacts very strangely with the War Caster feat, though -- at first glance it would seem to make part of the feat's benefits unnecessary, since a caster who uses holy symbols as foci can now cast S+M spells while holding a shield, so that character would not need the War Caster feat to do so. However, the War Caster feat would now allow that character to cast S spells without an M component normally, which the current ruling does not allow.
--
Pauper
I duno. To me, when a spell has both S and M components, it's generally the caster using S to manipulate M for the most part.
So a cleric/paladin using a "shield focus" is waiving their shield as part of the S requirement. A spell that does not include M, so strictly S (with perhaps V), needs hand gestures apart from otherwise manipulating an M. Therefore Warcaster makes sense to me. It's all about context.
mellored wrote:
ChrisCarlson wrote:
Just wondering, are there any spells that are 'M' but not 'S' ? (material without somatic)
I couldn't find one, but didn't run a complete search...
curiousdragon wrote:
In those cases, thematically, it still makes sense to me. Those spells use V to affect/empower M to trigger the magic. Rather than S to manipulate M.
Are there any spells with just M components, and neither S or V? That is what would probably not make any sense to me.
I have a hard time understanding why painting your holy symbol on your shield seems to work so differently from wearing it on a chain around your neck.
jaelis wrote:
Well, in one case you need a free hand, in the other you don't, is how it seems.
mellored wrote:
jaelis wrote:
Maybe I'm just confused. It sounds like you can cast a VSM spell while holding your mace and shield, if your holy symbol is painted on your shield. If your symbol is on a necklace, then you need to drop your mace and use your hand to manipulate the symbol.
jaelis wrote:
jaelis wrote:
So can I just incorporate my holy symbol into my mace? Or bolt it onto my gauntlet? If so, what's the point, why not just say you need to have your holy symbol visible? (If not, what's so special about shields?)
Tradition? I dunno. I encourage you to tweet the devs and ask.
But while you are pondering the possible reasons, expand it to all the rest of the foci in the game. What's so special about any of them? Significant?
jaelis wrote:
But again, be careful trying to dig too deeply into what "makes sense" and what doesn't.
As far as I can tell, bards can play a lute, harp, or even bagpipes, with only one hand. All while wielding a weapon in the other. So go figure...
abs1nth wrote:
jaelis wrote:
I guess shields are just special, what else can you say. Maybe the gods don't like two-weapon fighting, so they discourage it amongst clerics and paladins 
ChrisCarlson wrote:
I dunno. Does it?
I always figured that divine magic is not so much "casting a spell" as it is "beseeching a deity for them to cast a spell." In this case, what you are doing with the holy symbol is raising it to the heavens (or perhaps presenting it forcefully to your foes). Just having the symbol passively hanging around your neck is not enough - you have to actively draw attention to it.
In classic D&D, this was part of the differentiation between divine casters and arcane casters. Priests didn't have to worry about fancy gestures and footwork (which precluded the wearing of armour) - all they had to do was present their symbol and yell "Holy Lathander, aid thy faithful servant!".
I think the idea of a Bard NOT having to play their instrument to cast a spell is a fundamentally broken view of what a TRPG REALLY is. And the thought of the developers even considering adding that caveat makes my brain ache like the dickens. Who knows though, maybe this question has been asked so many times it deserves an errata...