i dont understand the perspective projection

im learning opengl from an online book

and i dont understand what the authors means from this headline “The Perspective Divide”
untill this one “Equation 4.2. Depth Computation” (including it)

this is the book

www.arcsynthesis.org/gltut/Positioning/Tut04%20Perspective%20Projection.html (remove *s)

I would appriciate if someone could help me understand it

anyone ? :{

What don’t you understand? Perspective? Homogeneous coordinates? gluPerspective()?

the link i gave you my main problem is to understand the text under the title “Camera Perspective” until the code of the vertex shader
I really dont understand why he did what he did I just dont understand what he explained and why he did the stuff he did maybe you could help me understand it