Can I use magic gifted by a deity if I'm not a paladin, warlock, or cleric of that deity?

Question

So, I'm wanting to create this homebrewed God called "The Crow Lord" (basically a less depressing and edgy version of the Raven Queen) and I'm fairly new to D&D and I'm a bit confused. My little-to-no experience in D&D has told me one thing (mainly my DM saying it): that you can't be a servant/follower of a deity unless you're a warlock, paladin, or cleric of that deity. Is that correct?

I want to make a rogue who worships the Crow Lord because crows pick up shiny stuff, and I feel like a thiefy-rogue would work and maybe that character could get advantage on stealth and sleight of hand checks because of that. I thought would fit nicely with that, but he just shot me down instantly.

Can I still use the magic gifted by the deity if I'm not a paladin, warlock, or cleric belonging to it? Or can you only worship a god and have your spells centered around that god (i.e. get in-game benefits like spells or buffs from that deity) if you're a cleric, paladin, or warlock?

Answer 1

Any character can worship a god, but only certain classes actually benefit from it in terms of game mechanics

Appendix B: Gods of the Multiverse (from the basic rules or PHB) describes that people may worship any god... or even multiple gods.

Many people in the worlds of D&D worship different gods at different times and circumstances. People in the Forgotten Realms, for example, might pray to Sune for luck in love, make an offering to Waukeen before heading to the market, and pray to appease Talos when a severe storm blows in—all in the same day.
...
And a few people dedicate themselves entirely to a single god, usually serving as a priest or champion of that god’s ideals.

Your DM determines which gods, if any, are worshiped in his or her campaign. From among the gods available, you can choose a single deity for your character to serve, worship, or pay lip service to. Or you can pick a few that your character prays to most often. ...

If you want to be a "servant of your god", that's perfectly fine. The Acolyte background models this quite well, without affecting which class you choose. So long as you aren't thinking of gaining magic through your worship, then any character you create can be a servant of one or more gods.

Receiving spells from your god is modelled by specific classes

However, when you start talking about spells, that's where the "class restrictions" come into things. Although your DM may be imposing different rules depending on their setting, generally speaking, if you want to get spells from a god, that means being a cleric:

Divine magic, as the name suggests, is the power of the gods, flowing from them into the world. Clerics are conduits for that power, manifesting it as miraculous effects. The gods don’t grant this power to everyone who seeks it, but only to those chosen to fulfill a high calling.

Paladins may also gain their powers from a god, although paladins in 5e aren't tied to gods as much as in previous editions:

Although many paladins are devoted to gods of good, a paladin’s power comes as much from a commitment to justice itself as it does from a god.

Warlocks aren't as clean cut; generally, warlocks make a deal, a pact, with an "otherworldly entity". Whilst your DM could decide that such a being is a god, generally the implication is that it's another sort of powerful being, such as a archdevil, an archfey, an angel, etc.

A warlock is defined by a pact with an otherworldly being. Sometimes the relationship between warlock and patron is like that of a cleric and a deity, though the beings that serve as patrons for warlocks are not gods.

Finally, I will also mention druids and rangers, who also gain magic from "divine" sources (the distinction between divine vs. arcane magic isn't really as much of a thing in 5e, but many D&D players use those terms), although they may also get their magic from "nature itself", so they don't strictly need a god like clerics do:

Druids revere nature above all, gaining their spells and other magical powers either from the force of nature itself or from a nature deity.

Thanks to their familiarity with the wilds, rangers acquire the ability to cast spells that harness nature’s power, much as a druid does.

In your case specifically, I'd recommend rogue with the Acolyte background

Based on the part of your question that says:

I want to make a rogue who worships the Crow Lord because crows pick up shiny stuff, and I feel like a thiefy-rogue would work and maybe that character could get advantage on stealth and sleight of hand checks because of that. I thought would fit nicely with that, but he just shot me down instantly.

If you picked the Acolyte background, as I mentioned above, this would give you that "servant of the gods" flavour but without clashing with your class choice of rogue, and if you let your DM know that you aren't expecting to get any divine magic out of this, it's just for flavour, hopefully he should be fine with that.

As a rogue, you get something called Expertise at 1st level. You are allowed to add your proficiency bonus twice instead of once to any two skills you are proficient in. If you make sure that you pick Stealth and Sleight of Hand as two of the skills you are proficient with (rogues are allowed to pick four from a subset of skills, as explained here; these four plus the two you get from the Acolyte background should see you with a total of 6 skill proficiencies at 1st level), then you can pick those two skills as your "Expertise" skills.

It's not quite advantage, but you will still be extra-good at Stealth and Sleight of Hand because of it, and you can still flavour it as "guidance from the Crow Lord", even though in terms of the game mechanics, it's just your rogue's base class feature and nothing to do with the gods at all (which should hopefully keep your DM happy).

Answer 2

Prior to the release of Mythic Odysseys of Theros, warlock, cleric, paladin, and sometimes druid were the canonical ways to gain spellcasting through some form of deity worship.

With the release of Mythic Odysseys of Theros, we have a campaign setting that includes mechanics for anyone to receive blessings and benefits from the gods. This system, the piety system, is described:

When you choose a god to worship as a beginning character, your piety score related to that god is 1. Your piety score increases by 1 when you do something to advance the god’s interests or behave in accordance with the god’s ideals. The gods expect great deeds from their champions, so your piety score typically increases only when you accomplish a significant goal (such as the completion of an adventure), make a significant sacrifice of your own self-interest, or otherwise when the DM sees fit. Each god’s description in this chapter includes a discussion of the god’s goals and ideals, which your DM uses to judge whether you earn an increase in your piety score. As a general rule, you can expect to increase your piety by 1 during most sessions of play, assuming that you are following your god’s tenets. The DM decides the amount of any increase or decrease, but a single deed typically changes your piety score by only 1 point in either direction unless your action is very significant.

As your piety score increases, greater divine blessings are conferred upon you.

And to answer your question:

Many of the blessings conferred by the gods in the Theros setting involve access to various spells.

It is important to note that these divine blessings give limited access to spellcasting because spellcasting is an incredibly powerful feature - the defining feature of many classes. To have full access to a non-caster class, and a robust repertoire of spells would be significantly imbalanced.

Also, to date, this piety system has only been written to apply to the Theros pantheon, similar rules have not been published for any other D&D 5e setting or pantheon.

But of course, a DM could allow a non-caster to receive some measure of spell casting ability from their god.

I would personally recommend factoring this in to the magic item economy of a campaign - say the god gifts their worshiper a weapon or ring that can cast a particular spell a number of times a day.

Answer 3

Any character can be a follower of a deity. This is not something that comes with a class, but something that is just a part of being a person. In many settings a character or person likely worships several different gods as a matter of course. That certainly doesn't mean they have different class levels for each deity!

Deities are described in more detail on page 293 of the Player's Handbook. That section is fairly explicit that deities usually have nothing to do with classes.

Most characters will receive no mechanical benefits from worshiping a deity. They receive no spells, special abilities, proficiencies, bonuses, or anything else. The choice is mostly to help create a character that is interesting to the player and appropriate for your campaign.

That being said, players may always choose to describe their abilities as being related to their deity. If your druid wants to worship a nature spirit, whose to say their spells don't come from the spirit? Maybe your fighter's martial prowess is partially due to worshiping an appropriate deity. Again, these are interesting descriptions, but don't influence the game mechanics in any way.