This need of an authoritative sanction is increased by considering, after M. Guizot's suggestion, that Christianity, though represented in prophecy as a kingdom, came into the world as an idea rather than an institution, and has had to wrap itself in clothing and fit itself with armour of its own providing, and to form the instruments and methods of its prosperity and warfare. If the developments, which have above been called _moral_, are to take place to any great extent, and without them it is difficult to see how Christianity can exist at all, if only its relations towards civil government have to be ascertained, or the qualifications for the profession of it have to be defined, surely an authority is necessary to impart decision to what is vague, and confidence to what is empirical, to ratify the successive steps of so elaborate a process, and to secure the validity of inferences which are to be made the premisses of more remote investigations. Tests, it is true, for ascertaining the correctness of developments in general may be drawn out, as I shall show in the sequel; but they are insufficient for the guidance of individuals in the case of so large and complicated a problem as Christianity, though they may aid our inquiries and support our conclusions in particular points. They are of a scientific and controversial, not of a practical character, and are instruments rather than warrants of right decisions. Moreover, they rather serve as answers to objections brought against the actual decisions of authority, than are proofs of the correctness of those decisions. While, then, on the one hand, it is probable that some means will be granted for ascertaining the legitimate and true developments of Revelation, it appears, on the other, that these means must of necessity be external to the developments themselves. 4. Reasons shall be given in this Section for concluding that, in proportion to the probability of true developments of doctrine and practice in the Divine Scheme, so is the probability also of the appointment in that scheme of an external authority to decide upon them, thereby separating them from the mass of mere human speculation, extravagance, corruption, and error, in and out of which they grow. This is the doctrine of the infallibility of the Church; for by infallibility I suppose is meant the power of deciding whether this, that, and a third, and any number of theological or ethical statements are true. 5.