Summary of comments of this office by Dom Schuster, in his work L'année liturgique.

Ever since the times of Saint Gregory, the holy quadragesimal fast begins on this day, which is also called in capite ieiunii (begining of the fast).

For the imposition of the ashes, the present missal still keeps a last vestige of the ceremony of the imposition of the canonical penance to public penitents. Towards the Ixth century, the discipline of public penance having come to an end, the Pope, the members of the clergy and the Roman people without distinction took themselves the place of the penitents of the past, and began henceforth to walk barefoot and their head sprinkled with ashes to the Basilica of Saint Sabina.

According to a medieval tradition, the ashes come from the olive branches blessed the preceding year. After having said four prayers over them, the priest sprinkles them with holy water and incenses them. Then he imposes them upon the head of the faithful, saying: "Remember that thou art dust, and to dust thou shalt return". During the imposition of the ashes, the «schola» of the cantors chants the following antiphons and responsories, taken from the night office in Lent:

a)    Let us change our garments for ashes and sackcloth: let us fast and lament before the Lord: for our God is plenteous in mercy to forgive our sins.

b)    Between the porch and the altar, the priests, the Lord's ministers, shall weep, and shall say: Spare, O Lord, spare Thy people; and shut not the mouths of them that sing to Thee, O Lord.

c)    Let us amend and do better for those things in which we have sinned through ignorance lest, suddenly prevented by the day of death, we seek time for peance, and be not able to find it. Attend, O Lord, and have mercy: for we have sinned against Thee.

"R/.  Attend, O Lord, and have mercy: for we have sinned against Thee. V/. Help us, O God, our Savior: and for the honor of Thy name, O Lord, deliver us. - Attend, O Lord. - Glory be. - Attend."

The Introït of the mass is taken from the 9th chapter of the book of Wisdom (verses 24-27), where it is affirmed that no sinner, no matter how impious he is, is ever excluded from divine mercy, who looks not upon the sin, the work of man, but upon the creature, the work and even the masterpiece of God: "Thous hast mercy upon all, O Lord, and hatest none of the things which Thou hast made, winking at the sins of men for the sake of repentance, and sparing them: for Thou art the Lord our God."

The Gradual responsory is taken from Psalm 56: "Have mercy on me, O God, have mercy on me, for my soul trusted in Thee. He hath sent from heave, and delivered me; He hath made them a reproach that trod upon me."

As a rule, the daily masses did not have a Tract; that which is today assigned by the missal, and which in Lent will be repeated thrice every week, has a more recent and irregular structure, since it is made of fragments of hemistichs from different psalms. It would seem that it was introduced into the liturgy by Pope Hadrian 1st, who ordered it to be recited upon a request from Charlemagne.

The Offertory is taken from Psalm 29: "I will extol Thee, O Lord, for Thous hast upheld me; and hast not made my enemies to rejoice over me: O Lord, I have cried to Thee, and Thou hast healed me."

The verse for the Communion psalm belongs to the graceful chant which is, as it were, the preface for the whole psalter: "He who shall meditate upon the law of the Lord, day and night, shall bring forth his fruit in due season." (Ps. I : 3)