After the Mass has properly begun, the priest begins to pray at the foot of the altar the forty-second psalms, “Judica me, Deus,” “Judge me, O God, and distinguish my cause from the nation that is not holy.” The antiphon, verse 4 of this same psalm, is recited as well: “Et introibo ad altare Dei,” “I shall go unto the altar of God, to the God who makes joyful my youth.”
Historically, this penitential act occurred at the beginning of Mass, at the foot of the altar, from the time when the Roman l liturgy spread into Gall-Frankish territory. On the other hand, the psalm did not gain an entrance into many arrangements through the later Middle Ages and after. Contemporary monastic liturgies such as the Carthusian and Dominican did not even insert Psalm 42 when they were established in the 13th century. Though whenever it was inserted, only a single verse was recited, Introibo ad altare Dei. Such was the case with the beginning of the psalm text, Dirigatur, Domine, oratio mea. The recitation of Psalm 42 is omitted in RequiemMasses, and in Masses de tempore during Holy Week. However, it is not omitted in festal or votive Masses during this time. Even when the psalm itself is omitted, the antiphon Introibo is said once. This is appropriate especially during Good Friday when no actual sacrifice is offered.
The antiphon Introibo contains the fundamental thought of the forty-second psalm which indicates the special point of view in which it is to be taken and recited. “It gives the key to the liturgical and mystical understanding of the psalm with regard to its application to the celebration.” It expresses the sentiment which animates the priest: he is powerfully attracted to the altar. The altar of God is a terrible place, yet there the priest stands, an unworthy servant of the Most High. “He remembers the words of St. Chrysostom: ‘When the priest calls upon the Holy Ghost and offers the tremendous Sacrifice: tell me in what rank should we place him? What purity shall we require of him, what reverence.’” He longs to ascend there to perform his sacred duty, to draw near to the Lord and to be united to Him. “By the words iuventutem meam the priest may indeed, also, acknowledge that from his early days God has been his delight and bestowed on him a thousand joys.” The lament includes a vow to give thanks in the Temple. It is a pure expression of yearning for God with no expectation of reward or other benefit. As such, its omission during periods of penitence comes as a result of the psalm’s intent, which is to banish sorrow and to awaken a joyful mood in the one praying. The approach to the altar is one of happiness and joy, and so the Syrians call the Mass simply Kurobho, “approach.”
St. Ambrose relates the meaning of this psalm with those who have just been baptized: “The cleansed people, rich with these adornments, hastens to the altar of Christ, saying: I will go to the altar of God, to God who makes glad my youth; for having laid aside the slough of ancient error, renewed with an eagle’s youth, it hastens to approach that heavenly feast. It comes, and seeing the holy altar arranged, cries out: You have prepared a table in my sight.”
These prayers “at the foot of the altar,” as Jungmann explains, only existed after the year 1000. This is because before the eleventh century, as a rule, there were no steps up to the altar—not even a platform. Yet by the ninth century, these prayers had been inserted:“On the way to the altar, Psalm 42 was spoken in common, and upon arrival at the altar two oration were added in conclusion, one of which is our Aufer a nobis. In the witnesses to this particular arrangement of the entry there are found in addition various apologiae, forerunners of our Confiteor, included in a variety of ways and in an assortment of forms. They are either added at the beginning or inserted somewhere in the middle or subjoined at the end. This arrangement quickly took the lead over other plans of a similar kind…Very seldom was there any clear transfer of the psalm to the altar steps. Often this transfer occurred because the chasuble was put on the altar, as was the custom especially at private Mass. In other cases the rubric was left indefinite. This diversity of practice corresponded to the variety in spatial arrangements. Often the distance from sacristy to altar was very short. In order not to prevent the psalm’s being said with proper care and to lend it greater importance, it was not begun until the steps were reached. This must have been the origin of the arrangement now found in the Missal of Pius V.”