I hear continually from sceptics on blogs and so forth that "Faith is irrational: it means believing in something with no good reason to do so."
Well, no it doesn't. You are talking historical nonsense. In the Gospels and the Pauline tradition, faith "does not mean intellectual acceptance of a creed or proposition, but loyalty, love, and devotion, something like what in Indian religion is known as bhakti." -- B.H. Streeter, The Rise of Christianity
Faith is necessary to arrive at religious understanding in the same way it is necessary to accomplish anything difficult, including making a scientific breakthrough, as noted by Michael Polanyi. One must be devoted to succeed. Faith is not the opposite of reason, but the only means by which reason can advance.