An illustrational form tells you through the intelligence immediately what the form is about, whereas a non-illustrational form works first upon sensation and then slowly leaks back into the fact.
To learn to see- to accustom the eye to calmness, to patience, and to allow things to come up to it; to defer judgment, and to acquire the habit of approaching and grasping an individual case from all sides. This is the first preparatory schooling of intellectuality. One must not respond immediately to a stimulus; one must acquire a command of the obstructing and isolating instincts.
And the first step, as you know, is always what matters most, particularly when we are dealing with those who are young and tender. That is the time when they are taking shape and when any impression we choose to make leaves a permanent mark.
In a race, the quickest runner can never overtake the slowest, since the pursuer must first reach the point whence the pursued started, so that the slower must always hold a lead.