Yes purpose depends on what you're going to read.

Purpose of getting healthy won't be found in a math book.
Nor will an economic book teach you about health.

So if your purpose includes math for example, what in your next activation layer are you going to learn.

Have you ever noticed that teachers usually teach one formula and then later teach the other? Their purpose is to build the foundation, what you need to know first, to build on the more difficult stage.

You learn better if you follow a similar pattern. First purpose would be to build the foundation and build on that.

So you long term goal may be to pass the course for a career in...
At this point you need to learn [subject / book] so that you can pass x stage exam.

And you can break it down to subsets by having a unique purpose for each activation layer,

So it might mean, your purpose is to learn/understand/ do the calculations/ write the formulas so "that I can" understand the next section of the course with ease. Or so that I can explain the formula to my friend, or, so that I can answer the instructors questions tomorrow, or so that I can start my project of.

Notice, you're purpose states how you will use the information.

If you have a long term goal and you're at the beginning of a course that last 3 or 4 years your long term purpose may lose it motivation to open the books because the amount you have to learn and how long it's going to take seems so huge, I don't recommend it as a go to purpose for activation.

Like the lessons, you need to chunk it down. Take smaller bites out of the elephant if you plan to eat it. Decide to take care of this part today another part tomorrow. And remind yourself the long term purpose from time to time to help you decide a shorter term purpose and don't be afraid to break it down further for each activation layer.

Each time you crack open a textbook you can have a different or slightly different purpose. That way you know at the end of the activation layer whether you have moved closer to your goal.

Alex