Final answer:
In Bach's church cantatas, intense ornamentation is predominantly found in the arias, expressing a rich and elaborate vocal line accompanied by intricate orchestral parts.
Step-by-step explanation:
In Johann Sebastian Bach's church cantatas, the ornamentation of the melody is most intense in the arias. These movements typically feature elaborate vocal lines that are rich in melodic embellishments. The orchestra often provides a supportive and intricate accompaniment that complements the vocal line's florid decoration.
The other movements, such as the opening chorus, recitatives, and chorales, have their own stylistic characteristics. The opening chorus might display complex counterpoint and dynamic interplay between voices, the recitatives serve to further the narrative in a more speech-like and less ornamented style, and the chorales are generally more straightforward in their harmonization and melodicism, allowing for congregational participation or reflection.