He is talking about a progression from teaching the Jambette ( leg stretching) to Spanish Walk (Combining the Leg Stretches with a Symmetrical forward Walk) to Passage (utilizing SW-Trot transition as a means to achieve the Passage).
In conventional Dressage Circles it is common to consider the Spanish Walk as non-classical- a circus trick that serves no purpose and that is vaguely frowned upon To this can reply: giving a good Spanish walk to a horse is not easy and is therefore worthy of interest. What is classical is to manage to give good Passage to any horse using gentle and intelligent methods.
" Horses with relatively inexpressive paces give very correct and even astonishing passages using this approach. This method also improves the passage of gifted horses giving it greater height, roundness and cadence."