You must understand that we are not saying one part but one line. This is because in Eyn Sof, blessed be He, there is no such thing as different parts. In His very perfection and complete limitlessness, He looks down upon the creation. This overall looking down is called a line, namely a ray, like a sunray emerging from the overall radiance of the sun.
...that enters into the hollow cavity... This is obvious in accordance with the image in the prophetic vision, as we have stated above. [From this point on until the end of the Opening, Ramchal’s commentary diverges from the phrasing of the initial proposition.]