Iúdica me, Deus,
et discérne causam meam
de gente non sancta:
ab hómine iníquo et dolóso
érue me.
Quia tu es, Deus, fortitúdo mea:
quare me repulísti,
et quare tristis incédo,
dum afflígit me inimícus?
Emítte lucem tuam et veritátem tuam:
ipsa me deduxérunt, et adduxérunt
in montem sanctum tuum
et in tabernácula tua.
Et introíbo ad altáre Dei:
ad Deum, qui lætíficat iuventútem meam.
Confitébor tibi in cíthara,
Deus, Deus meus:
quare tristis es, ánima mea,
et quare contúrbas me?
Spera in Deo, quóniam adhuc confitébor illi:
salutáre vultus mei, et Deus meus.

Psalm 42 (Latin Vulgate Psalm 43) is the hymn that traditionally opens the Mass as the Introitus. Its opening verses—“Iúdica me, Deus, et discérne causam meam de gente non santa… Et introíbō ad altáre Dei…”—form a concise petition for divine justice, a confession of trust in God’s strength, and a proclamation of worship.

The Latin version belongs to the Vulgate translation of the Hebrew Psalter (Psalm 42 in the Hebrew numbering, Psalm 43 in the Septuagint), compiled by St. Jerome in the fourth‑century and the text that has been handed down to the Tridentine liturgy.

The practice of singing a psalm fragment at the entrance of the Mass dates back to the early Western liturgy. As the Catholic Encyclopedia explains, the “Introitus” developed from the processional psalm that accompanied the celebrant’s entrance, a tradition already present in the sixth‑ to seventh‑century Roman “Ordo” and in the Gregorian Antiphonary. By the time of the Tridentine Missal (1570) the Introit had become a fixed element of every Mass, always consisting of an antiphon, a single verse of a psalm, and the Gloria Patri.

The Psalm is a profound expression of trust in divine justice, acknowledgment of God’s strength, and a proclamation of worship, echoing the Church’s ancient understanding of humanity’s place under God’s sovereign care.