Does this magic item require that you already have the ability to use the feature that it modifies?

Question

Last night the party was adventuring in Curse of Strahd.
In the previous session they had acquired the module-specific magic item

Icon of Ravenloft

This item can be attuned to by a good creature. In last night's session an NPC was able to attune to the item, unlocking its powers (emphasis mine):

Augury. You can use an action to cast an augury spell from the icon, with no material components required. Once used, this property can’t be used again until the next dawn.

Bane of the Undead. You can use the icon as a holy symbol while using the Turn Undead or Turn the Unholy feature. If you do so, increase the save DC by 2.

Cure Wounds. While holding the icon, you can take an action to heal one creature that you can see within 30 feet of you. The target regains 3d8 + 3 hit points, unless it is an undead, a construct, or a fiend. Once used, this property can’t be used again until the next dawn.

If I am reading this item correctly, anyone that can take an action can use Augury or Cure Wounds feature. The power is written in the format, 'if you have an action, you use the action and the item grants you this ability', even if you could not previously cast an augury or cure wounds, or even if you did not have Spellcasting ability.

However, it appears to me that what is granted by the Bane of the Undead feature is not the ability to Turn Undead, but rather a modification of that ability (+2 DC, use this as a holy symbol), to creatures that already have that feature. That is, in this sense "can use" and "can take" are granting you the ability, but "while using" requires that you already have the ability to do so. (This was important since the NPC in question did not inherently have the Turn Undead feature).

Am I interpreting this language correctly?

A good answer will show a similar example in a less ambiguous case. While this question is specifically about the 5e Curse of Strahd, I am open to an answer showing how that particular item 'is supposed to work' in a previous version of the module.

Answer 1

You are reading this correctly.

The Augury and Cure Wounds abilities of the item are granting its holder new actions they can take, and specify how those actions function. The Bane ability clearly does not grant you the ability to turn undead/unholy, but gives you a benefit when you use the item in conjunction with those abilities. If you don't have an action called "turn undead", then saying "You get a benefit when you use the icon to turn undead" is meaningless to you.

Keep in mind that "turn undead" isn't a spell or standard game rule, but a specific feature of a particular class. They wouldn't give you the ability to use it without either specifying what class it comes from and how to use it (like, say, "You can turn undead as if you were a 5th level Cleric"), or more likely, by simply reprinting the full text of the ability.