Father of Understanding
The Father of Understanding, is a being that the Templars pledge allegiance to and ask for guidance. In the Crusades, the Templars would usually sign his name before theirs in letters they wrote. During the Renaissance, Templars would often ask him for guidance as a greeting or at the end of a meeting:
"May the Father of Understanding guide us"
And in an e-mail, Alan Rikkin writes to Warren Vidic: "May The Father of Understanding guide you to success", meaning that the Templars still use the saying.
The Father of Understanding could also simply be a reference to the actual trait of understanding and acceptance, rather than an actual being (Such as Father Time and Mother Earth). In either case, it could simply represent the Templars' longing that their harsh means of attaining peace be understood as not as it appears, but as a necessary means of achieving a greatness beyond measure ("absolute peace").