Spiritual weapon claims that you make a melee spell attack against a target adjacent to your spiritual weapon. The rules for attacking while being unseen state that if the target cannot see you, you gain advantage on your attack against them.
Does this mean that if the enemy can't see you (such as if you were in complete darkness), but they can see your spiritual weapon, you gain advantage to attack them with the spiritual weapon bonus-action attack?
Best Answer
Rules As Written, you get advantage if you're unseen
The rules say:
"You", written here in these rules, means you, the caster.
If your target can't see you, you would get advantage against it even though they can see your spiritual weapon.
If you can't see your target, then you also get disadvantage against it and they cancel.
The third paragraph also applies: if you attack with your spiritual weapon, it will give away your position.
Clearly This Is Stupid
This is a loophole in the rules. A reasonable DM should house-rule that, when attacking with a spiritual weapon, you can get advantage if the spiritual weapon is unseen, but you cannot get advantage because the caster is unseen.