This video discusses the B-minor Sarabande's use of hemiola and Phrygian cadences, as well as the defining characteristics of a French sarabande in which the measures are paired, with a different accentuation on the second of the pair. There is also a discussion of how Bach's choice of key is related to the unequal temperament that was in use at the time.
The video then addresses how Bach encompasses all this within the "Doctrine of Affections" (Affektenlehre), which addresses the most important concern for musicians in Bach's time, namely that the purpose of music is to stir the listeners' emotions.
See Part one first
and Part three