Learn English – difference between phrases “at the moment” and “for the moment”

1. Prepare - is used to talk about something prepared for others to benefit from
2. Prepare for - is used to talk about somebody who will benefit from something prepared

"Prepare for the party" means that you didn't prepare the party (somebody else did) and you will benefit from that. "Prepare the party" means that you are the one who is preparing a party others will benefit from.

Example:

• I am preparing an exam. (I am the one who is creating the exam for others to pass)
• I am preparing for an exam. (Someone has created an exam that I need to pass)

There isn't much of a difference here. In sentence B you're using the sentence structure
{Do something} for {Reason}. Examples include:

• "Go to New Zealand for business"
• "Go home for your mother's birthday"
• "Read a book for fun"

Sentence A uses a specific kind of English idiomatic phrase {Go somewhere} on {type of time}. By 'type of time' I usually mean something like "business" or "vacation". Examples include:

• "Go to New Zealand on business"
• "Go to Florida on vacation"
• "Visit Australia on holiday"

but not

• "Go to New Zealand on February"

If you're ever unsure whether to use "on" or "for" in that type of sentence, "for" almost always works, and "on" is only correct for a specific few cases. For example, you could say "Go to New Zealand for February" and that would mean you were spending the entire month in New Zealand.