Schubert starts with a 2-bar phrase.
He then extends it into a longer phrase – repeating the b1 rhythm in b2
then the original 2-bar phrase,
followed by another longer phrase using b3 another variant of b1 and this final extension repeats to close the opening paragraph.
In the development section, Schubert plays around with the opening descending scale (a1) (page not displayed) and one could see the descending scales here as linked to that idea.
Now to the second subject group. 
At line 1 bar 1 Schubert turns d1 upside down to give d2 (not exactly – but the general shape is the same)
at line 2 bar 3 he extends the 2-bar phrase into 4 bars by changing d1 into d3, repeating it and tacking on a closing bar. (I realise I’ve mislabelled bar 3 as d1 not c1)
at line 3, d1 repeats in the bass 3 times then at line 4, d2 repeats in the bass 3 times
in line 6 after the 4 fz chords we have 2 bars of d3
and after the varied repeat of the 4 chords we have a d4, new, more playful variant of d3 c1
finally c1 twice in the bass give us a strong close. (sorry for the mislabelling as c1, d1)
The suggestion that I memorize these 2-pages led me to this analysis and I have gained more understanding from doing so and strengthened my memory of them. I recommend it.
My Life in Music 