The last Sunday in October was declared according to the will of Pope Pius XI. as the Mystery of the Kingship of Jesus Christ. This feast is no "eschatological" one -- Christ will rule at the end of times --, but today is a memorial directed against the "social errors". This error is laicism.
The Feast of Christ the King proclaims the right of Jesus Christ over the hearts of individuals, families and the social life. and the commonwealth.
Pope Pius XI. introduced the feast with the Encyclical "Quas Primas".
Why a Liturgical Feast to honor Christ the King? Pius XI wrote in his circular letter:
IN THE FIRST ENCYCLICAL LETTER which We addressed at the beginning of Our Pontificate to the Bishops of the universal Church, We referred to the chief causes of the difficulties under which mankind was laboring. And We remember saying that these manifold evils in the world were due to the fact that the majority of men had thrust Jesus Christ and his holy law out of their lives; that these had no place either in private affairs or in politics: and we said further, that as long as individuals and states refused to submit to the rule of our Savior, there would be no really hopeful prospect of a lasting peace among nations. Men must look for the peace of Christ in the Kingdom of Christ; and that We promised to do as far as lay in Our power. In the Kingdom of Christ, that is, it seemed to Us that peace could not be more effectually restored nor fixed upon a firmer basis than through the restoration of the Empire of Our Lord. We were led in the meantime to indulge the hope of a brighter future at the sight of a more widespread and keener interest evinced in Christ and his Church, the one Source of Salvation, a sign that men who had formerly spurned the rule of our Redeemer and had exiled themselves from his kingdom were preparing, and even hastening, to return to the duty of obedience.
Link to New Advent for the Encyclical...