D&D 5E Arcana cleric spell selection

[ghostofchristmaspast]

Can I pick a lower level spell for my Arcane Mastery?
If I pick Wish and it becomes my domain spell, does that mean I can never "loose" it (lorewise)?

ARCANE MASTERY:
At 17th level, you choose four spells from the wizard spell list, one from each of the following levels: 6th, 7th,8th, and 9th.
You add them to your list of domain spells. Like your other domain spells, they are always prepared and count as cleric spells for you.

 

[matskralc]

Can I pick a lower level spell for my Arcane Mastery?

As written, no, you must take a 6, 7, 8, and 9. As DM, I'd probably let you take lower level spells.

If I pick Wish and it becomes my domain spell, does that mean I can never "loose" it (lorewise)?

You can still lose the ability to cast it. It's just like a wizard would still always have it in his spellbook after losing the ability to cast it.