This hymn is used for Vespers on Sundays and Weekdays in Lent from the First Sunday in Lent through Passion Sunday in the Extraordinary Form of the Roman Breviary. It is used for Vespers on Sundays in Lent until Holy Week in the Ordinary Form. It was used for Vespers during Lent from Ash Wednesday to Passion Sunday in the Paris Breviary (1736). It was used for Lauds during the first three weeks on Lent in the Sarum Breviary. In the Ambrosian Breviary it is used for Vespers I of Sundays and Vespers & Lauds on Weekdays during Lent.
This is the original text of this hymn as it appears in Hymns Translated from the Parisian Breviary (1839):
Merciful Maker, hear our call,
On idle winds O let not all
Our prayers and tears be spent
In sacred Lent.
Thou who dost know each hidden part,
And with Thy sunbeam search the heart,
We unto Thee return,
O, do not spurn.
Much have we sinned, we confess,
Spare us! O, for our helplessness,
Upon us pity take,
For Thy Name’s sake.
May the stern rein of abstinence
So bring the body down, that thence
The soul may watch and pray
Her stains away.
Grant, One in Three, blest Trinity,
Grant, Three in One, blest Unity,
Our Lent may blessed prove
In fruits of love.
Words: Pope St. Gregory the Great (I), 6th Century; tr. Isaac R. Williams, 1839.
The original Latin text of this hymn may be found here.