I completely understand, and this is something that certain students struggle with.
It's important to understand, that the deities mentioned in the manual are taken from the "religion of Wicca" and are simply used as examples of how to use whatever deities you choose in your spells and rituals.
The deities used are just symbols for a higher power.
I had to choose some to use in the examples.
You may be interested in "tweaking" your spells along the lines of "Christian Wicca" which is VERY popular. I have MANY students who are Christian as well.
You can substitute any deity or deities you believe in, and use them in your spells.
For example, you may simply use "God" for everything and look at the spells as little prayers instead.
Spell casting is really just a fun and powerful form of "prayer" when you boil it down.
It all still works, energy is energy...and whatever means you use to access that energy has to line up with your deepest beliefs, whatever they are.