Viva Cristo Rey
The feast establishes the titles for Christ's royalty over men:
1) Christ is God and holds high power over everything;
2) Christ is our Redeemer, He made us His by His blood and now we belong to Him;
3) Christ is Head of the Church,
4) God bestowed upon Christ the nations of the world as his special possession and dominion.
We also learn that Christ's kingdom is for everybody who wants to be with Him, and it's endless. Most importantly, Christ's kingdom is not this world.
Prior to the Roman calendar reform in 1969, this feast was celebrated on the last Sunday of October. – catholicism.about.com