The Sutra

Still day 1! I have downloaded three books in the series "Modern Buddhism - The Path of Compassion and Wisdom"; Sutra, Tantra and Prayers for Daily Practice. All by Geshe Kelsang Gyatso. Just started on Sutra, a few hundred pages to go! I'm worried about the title of the third book, no Deity...so what are we praying to. Just looked at a website on secular Buddhism, seems to be some controversey about this, but as Buddhism doesn't have a deity I wonder why?