Grammar – The Use of “in” or “on” in Context

There are of course other ways to use the words "if not", but your example it is being used to introduce a condition to the sentence:

Shouldn't you have been at work today, if not, then it is alright.

The sentence seems fine. The only change I would make to be fussy would be to maybe use "that" instead of "it", depending on what it was you are saying is "alright" - the present situation, or the fact that you were not at work today.

Remember though that "if not" can be used in other ways. It can be used in place of "perhaps also", as in this example:

He has worked here for 5 years if not 6.

Yes, there can be a subtle difference in meaning.

When something does something to you, it generally means that it affects you in an objective way:

"What did the sun do to you?"
"It burned my skin."

When something does something for you, it generally means that it has some kind of beneficial effect:

"What did the sun do for you?"
"It made me feel warm and relaxed."

This same nuance could also be applied to your sentence about the Bible, although in a different way because of the additional use of like.

It is like the Bible to me.

This means that the book appears similar to the Bible. Whatever elements I think of when I think of the Bible, this other book also has those same elements.

This is more of an objective or intellectual statement. I may not have any particular interest in the Bible itself, but just be making a comparison.

It is like the Bible for me.

This means that it, like the Bible, is an important part of my life. The Bible affects my life and so does this book. Like the comforts I take from the Bible, I take some of those same comforts from this book. (It's also possible that I'm drawing a comparison between how the Bible affects other people—rather than myself—and that I'm saying that this book affects me in the same way.)

It is more of a personal and emotional statement.

However, because of the construction of this sentence, the to / for distinction will be even more subtle than in more direct comparisons (as with the example of the sun).

While the difference I describe may be intended or interpreted, most of the time the two words will be used interchangeably. (And the actual meaning will come from the context of the situation.)