In this short exchange one could see the entirety of salvation history. We rejected the joy that God gives in the Garden of Eden. In varying degrees, that joy is rejected any time we sin. We prefer the "joy" we provide for ourselves (which can never truly satisfy) rather than what God willed for us.
Christ came to change this situation. Through His sacrifice, that joy is once again given to humanity. Yet like before, we can choose to reject it. Contained in that statement is our own reversal of the devil's original offer to our first parents. While the world seeks their own desires and needs, we seek God's mercy.
Imploring that mercy, we ask to be judged according to that mercy. This is done by the priest and servers alternating responses in Psalm 42:
Judge me O God, and dinstiguish my cause from the nation that is not holy, deliver me from the unjust and deceitful man.What is requested is the sanctifying of the Church, a sanctification in the classic sense of the term. When something was sanctified, it was set apart. While everything else had multiple uses and functions, that which was sanctified was meant for one purpose, and one purpose only. The priest in saying this prayer is reminded of the fact that his very vocation was meant for the offering of the Eucharist. The faithful are reminded of their own priestly nature by baptism where their job is to offer their very existence to the Father.
For Thou art God, my strength: why hast Thou cast me off? and why do i go sorrowful whilst the enemy afflicteth me?
Send forth Thy light and Thy truth: they have conducted me and brought me unto Thy holy hill, and into Thy tabernacles.
And I will go in to the altar of God: to God who giveth joy to my youth.
To Thee o God, my God, I will give praise upon the harp; why art thou sad, O my soul, and why dost thou disquiet me?
Hope in God, for I will give praise to Him: the salvation of my countenance and my God.
Due to sin, we will stray from that vocation from time to time. Yet when that happens, we must always remember our job as Catholics: to approach the altar of God. The true altar is the Cross. Sometimes sacrifice is offered on the altar. Sometimes, the sacrifice of a contrite heart is offered as we approach the altar. Other times, it is a sacrifice of thanksgiving that is presented to the altar for the priest to offer. One way or another, our job is at the Holy Cross.
To remind us of our sinful nature and our refusal to be mastered by it, a verse from Psalm 123 is then recited:
Our help is in the name of the LordOnly through God's help can we expect to perform the job that is our calling, our vocation. Only through God can we receive true joy that comes about from fulfilling what we were created for. We are a people of the Cross, and only the Cross.
Who made heaven and earth