Thee falling fifths (“circle of fifths”) sequence is one of the most common in the baroque period. It occurs in three forms: (1) only 5/3 chords, (2) alternating 5/3 and 7 chords, (3) vice versa, or (4) only 7 chords. Notice how the dissonant 7 is always prepared (tied over) by common tone in the same voice before it occurs.
In the version that includes all 7 chords, the chords alternate being complete and incomplete (without the 5th).
