From the Wikipedia article: "Like Trinity Sunday and the Solemnity of Christ the King, it does not commemorate a particular event in Jesus' life. Instead it celebrates the Body and Blood of Christ really present in the Eucharist."
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To the chief Musician, A Psalm of David.
Hear my voice, O God, in my prayer: preserve my life from fear of the enemy. Hide me from the secret counsel of the wicked; from the insurrection of the workers of iniquity: Who whet their tongue like a sword, and bend their bows to shoot their arrows, even bitter words: That they may shoot in secret at the perfect: suddenly do they shoot at him, and fear not. They encourage themselves in an evil matter: they commune of laying snares privily; they say, Who shall see them? They search out iniquities; they accomplish a diligent search: both the inward thought of every one of them, and the heart, is deep.
But God shall shoot at them with an arrow; suddenly shall they be wounded. So they shall make their own tongue to fall upon themselves: all that see them shall flee away. And all men shall fear, and shall declare the work of God; for they shall wisely consider of his doing.
The righteous shall be glad in the LORD, and shall trust in him; and all the upright in heart shall glory.