I am only really familiar with D&D 5e, and whatever of D&D 3.5e I was exposed to whilst playing NWN2 some number of years back, but as far as I am aware, only druids have the spell flame blade on their spell list.
At face value, I can't see why this would be. Summoning a sword of fire seems like the sort of thing that sorcerers or warlocks should be able to do as well; in 5e at least, they can cast shadow blade, so why not flame blade?
Originally, I thought I wanted to know the designer-reasons behind this decision (and hence didn't ask it, as that's off topic), but then I realised that if such a designer's reason didn't include anything about the in-universe lore behind it, then I would be left rather dissatisfied (i.e. if it turns out that it's because, I don't know... Gary Gygax lost a bet back in the day, and that's the official reason, then technically my question would be answered, but that's not really what I'm looking for).
What I'm really after is why this makes sense from a lore perspective. Is there something special about forming a blade out of the element of fire that is specific to druids, or requires nature-y divine magic to perform? I accept that it is the case that, RAW, only druids can cast flame blade, but why does that make sense in-universe? If my sorcerer, the head of the Sorcerer's Guild, saw a fellow party member, a druid, cast flame blade, then my sorcerer may well wonder "why can't I, nor any sorcerer I've ever met, do that?". That's what I'm after.
So my questions are:
- Firstly, is my premise actually true? Across the editions of D&D (for which flame blade exists), has it always been a druid-exclusive spell? (Note that I'm excluding the ability to cast it as a racial spell, such as the Mephistopheles variant tiefling from Mordenkainen's Tome of Foes, and I'm also excluding bards learning it via Magical Secrets and other such hacks; this is about whether or not it's on a classes' default spell list);
- Secondly, the title question: why, from a lore perspective, are druids the only class who can cast flame blade? I'm looking for answers with citations from any official material from any edition of D&D.
If the answer is dependant on a specific setting, let's assume that the setting is the Forgotten Realms.