There are two illustrations of the relation between the spiritual and secular powers very common among papal writers. Gregory VII, at the beginning of his reign, compares them to the two eyes in a man's head. But he soon substitutes for this symbol of theoretical equality a comparison to the sun and moon, or to the soul and body, whereby he claims for the spiritual authority, as represented by the soul or the sun, the operative and illuminating power in the world, without and apart from which the temporal authority has no efficacy and scarcely any existence. An illustration equally common, but susceptible of more diverse interpretation, was drawn from the two swords offered to our Lord by His disciples just before the betrayal. It was St. Bernard who, taking up the idea of previous writers that these represented the sword of the flesh and the sword of the spirit respectively, first claimed that they both belonged to the Church, but that, while the latter was wielded immediately by St. Peter's successor, the injunction to the Apostle to put up in its sheath the sword of the flesh which he had drawn in defence of Christ, merely indicated that he was not to handle it himself. Consequently he had entrusted to lay hands this sword which denotes the temporal power. Both swords, however, still belonged to the Pope and typified his universal control. By virtue of his possession of the spiritual sword he can use spiritual means for supervising or correcting all secular acts. But although he should render to Caesar what is Caesar's, yet his material power over the temporal sword also justifies the Pope in intervening in temporal matters when necessity demands. This is the explanation of the much debated _Translatio Imperii,_ the transference of the imperial authority in 800 A.D. from the Greeks to the Franks. It is the Emperor to whom, in the first instance, the Pope has entrusted the secular sword; he is, in feudal phraseology, merely the chief vassal of the Pope. It is the unction and coronation of the Emperor by the Pope which confer the imperial power upon the Emperor Elect. The choice by the German nobles is a papal concession which may be recalled at any time. Hence, if the imperial throne is vacant, if there is a disputed election, or if the reigning Emperor is neglectful of his duties, it is for the Pope to act as guardian or as judge; and, of course, the powers which he can exercise in connection with the Empire he is still more justified in using against any lesser temporal prince. [Sidenote: Theory of Imperial party.]