Deeply conscious of his duty to instruct the nations, he issued a number of encyclicals, which were masterpieces of Latin com position, and embodied forcibly expressed ideas on all aspects of the life of the peoples. His Easter encyclical of 1878 dealt with the relation between the Church and civilization in general, and a year later he spoke in praise of St. Thomas Aquinas, for the ' study of whose doctrine an academy was set up, and whom he called the best leader for a renewal of philosophy. The famous encyclical on labour questions (Rerum novarum), issued in 1891, still continues to influence the modern world. It lays down a general programme for modern civilization, and points out that the possessing classes, including the employers, have important moral duties to fulfil, and that it is one of the first duties of society in general, in collaboration with the Church, which stands for reconciliation between the classes by virtue of its doctrine and the spirit of charity which inspires it, and with the State, whose duty it is to pass laws for the protection of the workers, to improve the position of the workers.
It was Leo's object to bring about harmonious collaboration be tween Church and State, without regard to what form of govern ment was adopted. The latter was a matter which did not concern the Church, so long as nothing was done which was contrary to justice. Other public utterances of this pope dealt with Social Democracy and freemasonry, the duties of the Chris tian citizen and the family, and religious questions. As a means of combating the rationalistic tendencies of scholarship, he en couraged the study of the Bible, and he founded several colleges for the Eastern clergy in order to promote unity between the churches. One of his main aims was to attain unity among the various Christian religious communities and Rome, and thus to restore the unity of the Christian faith.
Leo XIII. patronised art and learning to an extent which re calls the Renaissance popes. He was a great admirer of Dante, published his own poems, and founded a College of Literature. One of his greatest acts was to open the Vatican archives to students of all nations and denominations (188o), and the Biblio theca Leonina was founded for the same purpose. The pope was firmly convinced that the Church had nothing to fear from the investigation of truth, and it was his desire that the fullest light should be thrown on every detail of ecclesiastical and world history. Students of all nations, including England, set up his torical schools and research institutions in Rome, and have from that time onwards vied with one another in making use of this inexhaustible mine of knowledge for the advancement of learning. Leo encouraged archaeological and scientific studies, and re instituted the Vatican observatory. On the artistic side, he re built the apse of the Lateran basilica, and restored the Galleria dei Candelabri and the Borgia apartments.
In his relations with the newly established kingdom of Italy, the State which now contained the Vatican, Leo XIII. remained as a matter of principle in the same attitude as his predecessor, and avoided any official relations with the Quirinal, which was the royal residence. Following the example of Pius IX., he forbade Italian Catholics to take part in elections or to stand for the legislature, and demanded the restoration of the temporal sovereignty of the pope as a guarantee for the free exercise of spiritual power. A number of attempts were made to solve the Roman question, as it was called. But Leo XIII. and his secre tary of State Rampolla, who were friends of France, never for a moment entertained the idea of attaining their ends by bring ing about a war between the Powers and destroying the unity of Italy. They only considered peaceful methods. Negotiations were undertaken on the basis of the proposal that the popes, while giving up all further claims, should be granted effective sovereignty over a small territory. France, which was at that time an opponent of Italy, was in favour of an agreed solution ; Austria and Germany adopted an attitude of reserve, and Italian Liberalism, which was hostile to the pope, and instituted a celebration of the memory of Giordano Bruno in 1889 by way of demonstration, did everything in its power to prevent an agreement being reached. Leo XIII. was faced in Germany with the legislation which Bismarck had had adopted in Prussia as a result of the Kultur kampf. This legislation, with the severe police regulations and other material means of pressure which it instituted, set up a com plete system for the suppression of the freedom of the Church. The pope adopted a moderate and conciliatory attitude, and, with the support of the Catholic population of Germany, suc ceeded in obtaining the repeal of the legislation against the Church. Leo was appointed arbitrator in the dispute between Germany and Spain concerning the possession of the Caroline islands (1885). He also acted as arbitrator in a number of other cases, and thus renewed the former activities of the popes in international relations. Although he was specially friendly to France, his relations with that country were unsatisfactory, since measures were taken to bring about a complete separation of Church and State. A movement arose in England for union be tween the Anglican and Roman Churches, but Leo decided in the negative in the controversial question of the validity of the consecration of Anglican clergy.