I have been looking at the Sunni > Hanafi > Deoband version of Islam. They say that the following prayers should be offered by all adults every day:
Fajr
4 rakha (2 rakha sunnah, and 2 rakha fardh)
Dhohr
12 rakha (4 rakha sunnah, 4 rakha fardh, 2 rakha sunnah, and 2 rakha nafil)
Asr
8 rakha (4 rakha sunnah, and 4 rakha fardh)
Maghrib
7 rakha (3 rakha fardh, 2 rakha sunnah, and 2 rakha nafil)
Isha
17 rakha (4 rakha sunnah, 4 rakha fardh, 2 rakha sunnah, and 2 rakha nafil, 3 rakha witr, and 2 rakha nafil)
My question is, what is the purpose of the different sections of each prayer. When I say "sections", mean fajr has 4 rakhas with 2 sections, each of the sections has 2 rakhas each, 2 sunnahs and 2 fardha, what is the purpose of the 2 sunnahs and what is the purpose of the 2 fardhs?
My question is not about why some prayers are longer than others. For example, Dhohr consists of 12 rakhas in total and Fajr consists of 4 rakhas only, that is not what my question is about.
My question is, what is the purpose of the first set of 4 sunnahs, what is the purpose of the second set of 4 fardh, what is the purpose of the third set of 2 sunnah, and what is the purpose of the forth set of 2 nafil?
As this question is based on the Sunni > Hanafi > Deoband belief system, I would prefer their point of view if possible, but other point of views are fine if they have similarly structured daily prayers.