Measures 3 to 6

In measures 3 and 4 Bach presents a sequence based on the subject:

• The first four notes are transformed by augmentation (rhythmic values are doubled, a 16^th note becomes an 8^th note) and used as the bass in the sequence
• The subject is transformed by inversion (ascending intervals become descending intervals and viceversa) in the upper part:

They look like reflection on a mirror:

With these two motives, Bach creates a sequence that will modulate to G Major (dominant key). In measure 5 and 6 the subject appears in its original form in the bass (1), transformed by inversion in the upper voice (2) while the bass in eight notes reminds us of the augmented subject (3):