First the background, then the challenge.
In the beginning the was the Cleric, one of the big three of Original D&D. It occupied the middle ground, not as tough as a fighter, not as blasty as a magic-user, but had its bag of renewable hit points, and all was well, except that no one would play one except under duress. Good clerics cured light wounds, evil clerics caused light wounds, and all was right with the world. It really didn't matter who you worshiped, all good clerics came out of the same mold - plate and shield, blunt weapons, cure light wounds. It was an easy-access character class.
Then came Eldritch Wizardary and the Druid, which were a subclass of Cleric (meaning that they shared traits with the Cleric, mostly Wisdom as a core stat, which was important because it gave you an experience bump). But the Druids had a passel of new spells, only some of which overlapped with traditional Clerics. And there began the schism.
First Edition maintained the separate-but-equal natures of it with different spell description lists for the Druids and the Clerics, though a lot of the Druid list had - "See the clerical spell of the same name". But the idea was that, even though the Druid was a subclass, it required a full class treatment, and the sheer amount of work involved kept other godheads from getting into the act. You were a Good Cleric, Druid, or Evil Cleric. Neutral clerics were out there, but they existed in an existential detente with the Druids. Neutral Clerics could heal or harm, but since the hps involved were minimal, they were still sub-standard front line guys. But if you wanted your Cleric of Odin to wield a spear, well, no luck for you.
Second Edition mashed all the clerical/druidic spells together under the Priest class, and provided a door out of that problem - the priest of a specific mythos, of which the Druid was one type. So you had the Cleric and the example of the Druid. And the framework was created for making new mythos priests, a set of guidelines that might not get us fully from here to there.
And there the gates were open, and I have to take responsibility to for the next step. In FR Adventures, we did Priests of a Specific Mythos (renaming them Specialty Priests) for the entire bloody pantheon. Part of this was a response to specialty wizards, who were more limited in some schools but got bennies elsewhere (but schools of magic are another story). Now your Cleric could wield the weapon her god could used, and get a couple other cool powers. Now the explosion starts with a plethora of Clerical demi-classes. And while the base-line cleric was still a default, the Specialty Priest was an advanced character class, in that it required some thought and understanding of both the world and style of campaign before you went in.
Third Edition abandoned the default cleric entirely. Now you were expected to pick up your god at the get-go, and you get tailored powers for it. Running a cleric, once the sleepy backwater of play, now had a lot of investment at the get-go. And they solved the problem of customizing the gods for your campaign by granting the powers not by god, but by portfolio (another Realms wrinkle). So if you worshiped a god with the fire portfolio, you got fire buffs. Extremely popular in the day were gods that had the luck portfolio, which allowed you to, once a day, to force the reroll of a d20. We used to call that cheesy. These days we call them halflings.
And now, 4E. You can Channel Divinity class feature. Channeling Divinity opens up certain new abilities to your character. Some of them are available to all Clerics - Turn Undead and a limited Bless (Divine Fortune). But you also can get additional feats based on the god you worship. Now you choose your god, and your god grants you something specific in return. If you don't worship one of the gods covered in the book (or they don't exist in your campaign, you have a problem.
And that's my prob at the moment - I'm putting together a Kobold Cleric. I don't have any Kobold gods in the core books, so the whole Channel Divinity thing is up in the air. And there is no longer a "default cleric" that I can run back to.
I have three options, and I will talk about them next time.