Commentary Purg XIV 14-15

Guido's amazement at Dante's condition does two things quickly and neatly; it shows that he (and Rinieri) are not envious of his condition and it allows Dante not to have to insist pridefully on his uniqueness, something that Guido has done for him.  Once we find out who these two are, we realize that these now fraternal souls were, on earth, a Ghibelline (Guido) and a Guelph (Rinieri).  These details may remind us of the far less fraternal interaction between Farinata (a Ghibelline) and Cavalcante (a Guelph) in Inferno X.