First of all, what creates loyalty in a customer?
It's not logic, it's emotion.
Therefore, the ultimate goal of an outstanding copy is to evoke an emotional response from the customer.
What kind of feeling can the product create in the person?
For instance, if it's a fitness course, it should focus on how the person will feel proud, energetic, and confident after completing the course.
Instead of making generic statements like "buy this course and feel amazing", the copy should be more personalized.
For example, "Wouldn't you love to wake up in the morning feeling energized, take that first look in the mirror and feel proud of how your body looks and feels?"
The closer the copy is to the customer, the better.
There are certainly better ways to phrase that sentence, but I just wanted to give you a general idea of the psychology behind a successful copy that converts.
I hope this information helps you decide if I'm the right fit for you.
Thank you for taking the time to read this.
Marin