In Cantatas, the Aria (Air) was used to represent God's voice. It is no surprise that Bach Arias have reached such magnificence especially when you consider that he was a deeply religious person and his knowledge of music allowed him to express these feelings beyond the norm. Bach Arias are among the few pieces that can make a human being shiver from head to toes and the German master seemed to have the key to achieve the depth and breath of these amazing works.
I consider the Arioso to be the most profound piece ever written along with the Air on the G string.