How the Rebel Motif is Derived from the Main Theme

Two of the more important musical elements of "A New Hope" are the Main theme and the Rebel motif - and they are clearly related. At the end of the first phrase of the Main theme are the chords A-flat, G, and F. These same chords are used near the end of the Rebel motif, indicated in the graphic  below with red lines.

Furthermore, the chord progressions used throughout the Rebel motif are identical to the one borrowed from the Main theme. The technical description would be two major chords, the latter a minor third lower pitched than the first. In the Main theme, the G chord functions as a neighbor chord; and in the Rebel motif, the G chord functions as a passing chord, which is to say that in both instances the G chords are of secondary importance. Rather, the chords of primary importance are A-flat and F - and there is the seminal pattern of two major chords where the second is a minor third lower.

The Rebel motif then takes that descending minor third and uses it a total of four times (as indicated below with red boxes) - thrice from F to D, plus the A-flat to F borrowed from the Main theme.

Lastly, also notice that the final two boxes overlap - the F serves as both the bottom of the progression from A-flat to F, and as the top of the progression from F to D.

All of this is to say that the heroic Main theme is strongly related to the Rebel motif. In other words, from the music alone we know that the Rebels are the "good guys".