I'm studying diatonic modulation via example (e) in Unit 26 of "Harmony & Voice Leading" by Aldwell and Schachter and need some clarification. The progression moves from an F major to an E7 - Am cadence. While I grasp the overall concept of leading to an authentic cadence, I'm struggling to distinguish between the functional chords driving the modulation and the decorative ones.
Could someone please explain the inclusion of non-essential chords within this progression? I'm interested in understanding the progression as a whole, as each chord contributes to the progression's flow and harmonic richness.