This hymn was used for Nocturns on the Feast of the Lord’s Circumcision (Octave of Christmas) in the Paris Breviary(1736).
O happy day, when first was poured
The blood of our redeeming Lord!
O happy day, when first began
His sufferings for sinful man!
Just entered on this world of woe,
His blood already learned to flow;
His future death was thus expressed,
And thus His early love confessed.
From Heaven descending to fulfill
The mandates of His Father’s will,
E’en now behold the victim lie,
The Lamb of God, prepared to die!
Lord, circumcise our hearts, we pray,
Our fleshly natures purge away;
Thy name, Thy likeness may they bear:
Yea, stamp Thy holy image there!
O Lord, the virgin born, to Thee
Eternal praise and glory be,
Whom with the Father we adore,
And Holy Ghost forevermore. Amen.
The original Latin text of this hymn may be found here.