Beati Mundo Corde - Gregorian Chant on the Beatitudes of the Sermon on the Mount
As I am sure you will quickly recognize, this is a hymn from the Beatitudes of Christ in His sermon on the mount. The three beatitudes from Matthew 5:8-10 are:
Beati mundo corde: quoniam ipsi Deum videbunt.
Blessed are the clean of heart; they shall see God.
Beati pacifici: quoniam filii Dei vocabuntur.
Blessed are the peace-makers; they shall be counted the children of God.
Beati qui persecutionem patiuntur propter justitiam: quoniam ipsorum est regnum caelorum.
Blessed are those who suffer persecution in the cause of right; the kingdom of heaven is theirs.