[kaels]

Basically, you have 2 problems with how you're referring to your saved variables. See here:

function events:UNIT_POWER(source,type)
    if source == "player" and type == "HOLY_POWER" then
        local power = UnitPower("player",9)
 
        if power == 1 then
            texture:SetTexture(self.db.textureSelect.."1.tga")
            frame:Show()
 
        elseif power == 2 then
            texture:SetTexture(self.db.textureSelect.."2.tga")
            frame:Show()
 
        elseif power == 3 then
            texture:SetTexture(self.db.textureSelect.."3.tga")
            frame:Show()
 
        elseif power == 0 then
            frame:Hide()
        end
    end
end

"self" in this function refers to "events", so it's trying to access events.db instead of HolyPowerIndicator.db.

The other problem is that HolyPowerIndicator.db is defined here:

self.db = LibStub("AceDB-3.0"):New("HolyPowerIndicatorDB", defaults, "Default")

to refer to the table "defaults", but the data you're actually interested in is in defaults.profile.

So basically you need to replace all instances of "self.db" (ouside of your OnInitialize function) with "HolyPowerIndicator.db.profile".