Pope Pius XI universally instituted The Feast of Christ the King in 1925 in his encyclical Quas Primas. Pope Pius connected the denial of Christ as king to the rise of secularism. At the time of Quas Primas, secularism was on the rise, and many Christians, even Catholics, were doubting Christ's authority, as well as the Church's, and even doubting Christ's existence. Pius XI, and the rest of the Christian world, witnessed the rise of dictatorships in Europe, and saw Catholics being taken in by these earthly leaders. Just as the Feast of Corpus Christi was instituted when devotion to the Eucharist was at a low point, the Feast of Christ the King was instituted during a time when respect for Christ and the Church was waning, when the feast was most needed. In fact, it is still needed today, as these problems have not vanished, but instead have worsened.Pius hoped the institution of the feast would have various effects. They were:
1. That nations would see that the Church has the right to freedom, and immunity from the state (Quas Primas, 32).Today, the same distrust of authority exists, although the problem has gotten worse. Individualism has been embraced to such an extreme, that for many, the only authority is the individual self. The idea of Christ as ruler is rejected in such a strongly individualistic system. Also, many balk at the idea of kings and queens, believing them to be oppressive. Some even reject the titles of "lord" and "king" for Christ because they believe that such titles are borrowed from oppressive systems of government. However true these statements might be (some kings have been oppressive), these individuals miss the point: Christ's kingship is one of humility and service. Jesus said:
2. That leaders and nations would see that they are bound to give respect to Christ (Quas Primas, 31).
3. That the faithful would gain strength and courage from the celebration of the feast, as we are reminded that Christ must reign in our hearts, minds, wills, and bodies (Quas Primas, 33).
You know that those who are recognized as rulers over the Gentiles lord it over them, and their great ones make their authority over them felt. But it shall not be so among you. Rather, whoever wishes to become great among you will be your servant; whoever wishes to be first among you will be the slave of all. For the Son of Man did not come to be served, but to serve, and to give his life as a ransom for many (Mark 10:42-45, NAB).and
Pilate said to Jesus, "Are you the King of the Jews?"... Jesus answered, "My kingdom does not belong to this world. If my kingdom did belong to this world, my attendants would be fighting to keep me from being handed over to the Jews. But as it is, my kingdom is not here." So Pilate said to him, "Then you are a king?" Jesus answered, "You say I am a king. For this I was born and for this I came into the world,to testify to the truth (John 18:33b, 36-37).Thus, Jesus knew the oppressive nature of secular kings, and in contrast to them, he connected his role as king to humble service, and commanded his followers to be servants as well. In other passages of Scripture, his kingdom is tied to his suffering and death. While Christ is coming to judge the nations, his teachings spell out a kingdom of justice and judgment balanced with radical love, mercy, peace, and forgiveness. When we celebrate Christ as King, we are not celebrating an oppressive ruler, but one willing to die for humanity and whose "loving-kindness endures forever." Christ is the king that gives us true freedom, freedom in Him. Thus we must never forget that Christ radically redefined and transformed the concept of kingship.
Christ the King Sunday used to be celebrated on the last Sunday of October, but since the calendar reforms of 1969, the feast falls on the last Sunday of Ordinary Time, which is the Sunday before Advent. It is fitting that the feast celebrating Christ's kingship is observed right before Advent, when we liturgically wait for the promised Messiah (King).
Source: All About Christ the King Sunday