Can a spiritual weapon be moved through walls?

Question

Reading How does a Spiritual Weapon interact with illusions of creatures when it is moved? made me wonder - can a spiritual weapon be moved through walls?

The description of the spell reads (emphasis mine):

You create a floating, spectral weapon within range that lasts for the duration or until you cast this spell again. When you cast the spell, you can make a melee spell attack against a creature within 5 feet of the weapon. On a hit, the target takes force damage equal to 1d8 + your spellcasting ability modifier.

As a bonus action on your turn, you can move the weapon up to 20 feet and repeat the attack against a creature within 5 feet of it.

Spells typically require line-of-effect when cast, which would prevent you from conjuring the weapon on the other side of a wall. Does that have any bearing on moving the weapon through the wall? Additionally...

1. Do you need to be able to see through the wall (for example, with a warlock's Ghostly Gaze invocation) to move the weapon through it?
2. Would you also be able to move the weapon through if you can only see the other side of the wall (for example, seeing through a familiar's eyes)?
3. Assuming that you are permitted by the rules to move a spiritual weapon through walls, can the weapon physically pass through? Can it remain in the wall?

Answer 1

It depends on the DM's discretion

Normally, the rules on targeting would seem to dictate that you must have LOS to where you want to move the weapon:

To target something, you must have a clear path to it, so it can't be behind total cover. If you place an area of effect at a point that you can't see and an obstruction, such as a wall, is between you and that point, the point of origin comes into being on the near side of that obstruction.

However, as this unofficial tweet says, the Spiritual weapon does not adhere to the rules on targeting or positioning of spell effects:

The spell doesn't require you to see its target. It follows the normal rules for attacking a target you can't see.

Also worth pointing out is the fact that there are creatures that possess the Incorporeal Movement feature which states:

Incorporeal Movement

The specter can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

While the spiritual weapon is at least visually similar to these creatures, it is not a creature and the rules on the weapon do not explicitly confer the Incorporeal status. Since spells are limited in effect to what their rules text says they are allowed to do, there is no textual support for allowing movement through walls.

However, allowing movement through walls is not particularly game breaking and is at least thematically in keeping with the nature of the weapon as a spectral entity. It is therefore entirely reasonable that a DM could allow movement through walls. It is probably not reasonable to allow it to stop within a wall based on the Incorporeal attribute of those kinds of creatures, however.

Answer 2

The case for: Yes; spiritual weapon can move through walls.

As you point out, the description indicates it's spectral, which is "of or a like a ghost." We have ghosts, and they have incorporeal movement. Which allows them to "move through other creatures and objects."

Implications for Attacking

Once the weapon is somewhere the caster cannot observe, all creatures present are hidden or unknown to them. Attacking without knowing a creature is present is covered by "Unseen attackers and targets" of the Player's Handbook. Here are some posts that are relevant to that scenario:

• How does an NPC guess where an invisible PC is when attacking?

• How do you target someone in magical darkness?

Implications & Short Answers

Do you need to be able to see through the wall (for example, with a warlock's Ghostly Gaze invocation) to move the weapon through it?

No.

Would you also be able to move the weapon through if you can only see the other side of the wall (for example, seeing through a familiar's eyes)?

No.

Assuming that you are permitted by the rules to move a spiritual weapon through walls, can the weapon physically pass through? Can it remain in the wall?

Yes.