What is the virtue of calling both the Adhan and Iqamah compared to only reciting the Iqamah?

Primary text

If a man is in a land and recites only the Iqamah, two angels pray behind him. However, if he calls both the Adhan and the Iqamah, angels whose numbers cannot be counted pray behind him, bowing, prostrating, and saying 'Amin' to his supplication. Sa'id ibn al-Musayyib stated that the number of angels praying behind him would be like mountains.