To understand the logic behind today's idea, we need to pay careful attention to paragraph 1. The basic logic there is that fear is rooted in a false view of ourselves, which then projects a false world. Let's look at this more closely.
Fear is basically the expectation of being attacked by the world. That is the perception of the world that Jesus is talking about here: "The world's about to attack me."
And what he's saying, of course, is that this is the projection of a false self-perception. This naturally raises the question, what is this false view of ourselves? What view of ourselves would project a world that constantly threatens to attack us?
Based on hints in paragraph 2, and based on the Course's general teaching, two candidates suggest themselves.
The first is the self-perception that says we are vulnerable humans who are prone to suffering, rather than all-powerful Sons of God who cannot be hurt. The belief "I can be hurt" would naturally project a world that can hurt us.
The second is the self-perception that says we are sinful human who deserve to suffer, rather than holy Sons of God who deserve only endless love. The belief "I deserve to be hurt" would naturally project a world that does hurt us.
So this lesson is saying that it is only our belief that "I can be hurt and I should be hurt" that gives rise to a world that seems constantly poised to hurt us.
This puts us in a position to understand the real thrust of this lesson's teaching: You can't be hurt. And you don't deserve to be hurt. Therefore, the world you see that's poised to hurt you is false; indeed, impossible. It is an illusion, a deceptive appearance. Even more, it is self-deception. You are kidding yourself to think you can be hurt. Somewhere inside, you know better.
Therefore, your fears are actually "foolish" (2:1). They are laughable. How could God allow His Own Son to suffer? Such parental negligence makes sense only with fallible human parents, not with the perfect Divine Parent. If you're His Son, you are safe forever.
Our goal today, then, is to realize that we are the Sons of God, to recognize our invulnerable nature. This means forgiving ourselves ("Let us forgive him in Your Name"). Only when we are willing to do this will we recognize our holiness, and thus recognize that we have never deserved to be hurt. And only then will we see a world that cannot hurt us.
On the practical side, notice that the lesson is focused on "not…in any form" (title) or "does not matter what the form" (2:4). So our goal is to realize that the little fears and the big fears are all the same—equally unjustified.
Therefore, try to be vigilant all day for any instance of fear, from vague worry to genuine terror. When you notice an instance of fear, no matter how mild or severe, repeat the line in this specific way:
Fear is not justified in this form,
because fear is not justified in any form.