So D&D has always had this thing where wizards have to research or seize their spells from others, but clerics automatically get access to all spells of each new spell level. (4e is the exception, since it had a totally different approach to spell levels.) Everything else about the two classes' approach to preparing and casting spells is basically the same, though. I can't help but find this disappointing - there's a huge opportunity to get clerics interested in adventures to gain new spells, but any such additions have to come from outside the published material.
I do kind of get why it's done that way, from a nominally simulationist perspective. D&D's default assumption is that wizards are solitary and competitive, while clerics operate within the structure of organized religion and have obligations (these are great for adventure hooks, so I can't complain) and a support network. That infrastructure has had centuries to codify and duplicate all of the prayer-books, and then provide and teach those prayers to novices. Further, arcane magic is supposed to be arcane, esoteric, and difficult (hence the whole "memorization" thing, because D&D copied every part of Vance's wizards), while divine magic is a prayer, either in the common tongue or in some cognate of Church Latin. Given those thematic assumptions, there isn't a lot of room to make divine magic difficult or hidden. Since questing and research for spells are things I want in the game, this is a post about an alternate theme and explanation for divine magic.
To get to that point, let's talk about the word channeling. Many, many systems of magic describe the spellcaster channeling and shaping energy from elsewhere, including the D&D Next cleric's Channel Divinity powers. The word suggests two things: the image of a river of power (with tributaries, stream beds, and so on), and immediacy. On the latter note, when magic is described as channeled, I expect the spellcaster to make very few decisions beforehand. The caster decides what to cast and the relative power with which to cast it (if that is variable - metamagic is what I have in mind here) at the moment she exercises that power in the world. The decisions are less strategic and more tactical.
The image of the river suggests that the power is more straightforward in its function than subtle, wherever possible. If power is the water, the spellcaster must be the earth of the river itself; something about the spellcaster is the limit to how much power can move from the headwaters (the godhead, in the cleric's presumptive case) to the ocean-that-is-the-world. What happens when the volume of water is greater than the riverbed? A flood, reshaping of the riverbed, and erosion: uncontrolled alteration of the world outside the caster's body and soul. Many channeling systems include overchanneling mechanics, drawing more power than the caster can manage or tolerate, with some kind of detrimental effect.
Remembering that D&D clerics are the warrior clergy (as opposed, presumably, to some NPC stay-in-the-temple, non-adventuring priesthood), I think it makes sense that clerics enter into an oath of fealty that treats the god or gods as liege-lords. The vassal pledges loyalty, fidelity, and service; in exchange the liege-lord pledges protection and loyalty. The cleric becomes a knight in the god's army. If a novice cleric is the priestly parallel of a new-made knight, then the lord should grant arms, armor, and spurs rather than lands. (This assumes the cleric makes his vows to the god directly, rather than to a senior cleric who is the parallel of a duke, count, or baron... there's an interesting set of ideas there too, but one thing at a time.)
Digression: This opens the door once again to the discussion of where the warrior-cleric stops and the paladin begins. I don't have an answer to present on that question right now. Ultimately the classes interest me most when they justify their existence through both mechanical and thematic distinction, but I would be okay with treating the paladin as a multi-class cleric build, or as a cleric class + background + specialty combination.
The "arms" that the god grants are the at-will attack spells - in current writing, this includes only the lance of faith, but that's nicely on-point. I like the idea that in return for the cleric's vow, the gods promise, "We shall never abandon you, nor leave you helpless in the midst of Our enemies. Therefore take up the Lance of Faith and the Song of Battle, for Our enemies gather against Us." Continuing the parallel, knights had the authority to carry out justice in the lord's name. As an envoy plenipotentiary (yeah, I just like the word), the cleric has the authority and capacity to channel divine power directly into the world, and develops that power further over time.
So the gods grant the Lance of Faith and the Song of Battle (see below) directly. Where do other spells come from, and how does a cleric pursue them through adventuring means? Since I'm following the idea that all clerical spells are a channeling of divine power (secondary idea: what if spell preparation is functionally the parallel of going before the god and seeking a writ to carry out some future exercise of power?), new ways of channeling come from either adding impeding objects to the riverbed, or from carving a new path into the earth. Either of these might be sufficient metaphors to match the image, and both suggest an event of major spiritual impact.
Every temple that has the capacity to train novices (this might not be all temples - maybe only cathedrals and monasteries have the spiritual authority to create new clerics) has relics from holy people and deeds of ages past: fingerbones, chalices, ceremonial garb, and so on. By taking time to meditate on or otherwise spiritually engage with the object, the cleric undergoes a traumatic (probably cathartic) internal experience; the wisdom of the saint's life or the pathos of the heroic, miraculous deed reshapes the cleric's soul. Each location generally has one relic that grants healing ability (since healer saints and miracles of healing are among the most common... and because I want to support clerical healing in gameplay), and a few other relics that grant various expressions of divine power. It doesn't take long - a few days of in-game time, and maybe a scene or two at the table - to complete everything that the starting holy site can teach. (On a D&D Next note, I'd point out that this could be an interesting couple of encounters for apprentice-level PCs.)
The rest of the powers, then, come from quests and pilgrimages. On a pilgrimage, the cleric is pretty much dragging the party across the countryside so that she can learn a new way to channel. Presumably some interesting things happen on the way. Alternately, a few weeks or a month of travel substitutes for training time. Some of these relics are, by their nature, not portable (Mecca, Canterbury Cathedral, Calvary), or are so valued by their current owner that the cleric has to go to them, not the other way around (the Shroud of Turin). Each of these might teach one or more ways of channeling to the cleric - and seriously, if you can't come up with an interesting story while traveling to Canterbury, I don't know what to tell you.
The Song of Battle
On a related note, both of the players in my Aurikesh campaign who had initially rolled up clerics have dropped those characters, one in favor of a fighter and one in favor of an outlander. They have their own reasons for making this decision, but the essence of the matter from what they've said is that the cleric isn't very exciting in its current incarnation. There's some pressure for the cleric to reserve all spell slots and Channeling for healing (and given the way the campaign's flow works, this means they end a lot of days with unspent spell slots, saved against emergencies). They both built laser clerics, which touches on a really weird part of D&D Next's design: melee clerics can cast a Swift Action spell (such as healing or buffing) and still make a melee attack, but ranged clerics cannot both cast a Swift Action spell and fire off a lance of faith, which is their basic attack. I think it's fine if they can't use a bigger attack spell, but casting a lance of faith (or just about any clerical cantrip) should be treated no differently than a weapon attack in terms of action economy.
The other problem - and this extends to most classes at the moment - is that if you're not using a per-encounter or per-day resource, you really only have one attack option. This really deserves its own post, but the problem with this is that the player often isn't making an interesting choice for her action. All characters having at least two at-will attacks is one of the unsung heroes of 4e's design, and I'm disappointed to see that get lost in D&D Next. My solution, then, is to offer another attack cantrip for clerics: the Song of Battle.
"I invoke the names of Sioctana-Who-Defends and Talend-Who-Exalts-In-War, that our enemies shall falter and our ally (Name) shall prevail." Casting Time: 1 action. Effect: Choose a creature that you can see within 25 feet of you. The target must succeed on a Wisdom saving throw, or it takes 1d6 psychic damage. Choose an ally within 25 feet of you; that ally deals +1d6 radiant damage with her first successful attack before the beginning of your next turn. At Higher Levels: The spell's damage and damage bonus granted to an ally each increase by 1d6 which you reach a caster level of 5th (2d6), 10th (3d6), 15th (4d6), and 20th (5d6).
My thinking here is that lance of faith is difficult to create variations on, since it has only its damage component, its range, and the fact that it targets Dexterity. To add a variant function, I needed to reduce damage output to the primary target. In exchange for this, the caster's ally deals additional damage, if and only if the ally hits with an attack in the following round; thus the damage bonus probably doesn't apply about 25-33% of the time. That seems about fair to me; along with the difference in range and damage types, I think the cleric would find that lance of faith and song of battle were each worth using at different times.
I haven't fully explored the idea of clerical magic as channeling here, but that represents a massive rework of the rules for the cleric class and spell list, so that will have to wait for some future post (and quite a bit more spare time). I hope that the WotC designers put a lot more work into the cleric - right now, D&D Next represents a huge step back in the interest and variety of the cleric class. I hope that invokers and avengers both see support in this edition, as they are mechanically and thematically some of the most compelling classes of 4e.