Psalm 51, known as the Miserere (from the Latin Miserere mei, Deus – “Have mercy on me, O God”), is one of the most poignant penitential psalms in Scripture. The provided text is its responsorial form, with the refrain “Have mercy on us, O Lord, for we have sinned” (or similar variants like “Be merciful, O Lord, for we have sinned”) interspersed among key verses.

Its origins lie in ancient Israel. Tradition attributes it to King David, linking it via the psalm's superscription to Nathan's rebuke after David's sin with Bathsheba and the murder of Uriah (2 Samuel 11–12), circa 1000 BCE. This heading may be a later interpretive addition; scholars debate its precise dating, with linguistic evidence pointing possibly to pre-exilic or post-exilic composition. Nonetheless, the psalm powerfully conveys contrition, recognition of sin primarily against God (“Against you, you alone, have I sinned”), and a heartfelt plea for inner transformation – “Create in me a pure heart, O God; renew a steadfast spirit within me.”

In Christian liturgy, Psalm 51 is one of the seven Penitential Psalms and holds deep significance for Lent, the season of repentance and preparation for Easter. It opens daily prayer in the Liturgy of the Hours and inspires renowned settings, such as Allegri's polyphonic Miserere.

For the Mass on the First Sunday of Lent (Year A) in the liturgy, this psalm is the Responsorial Psalm (Psalm 51:3-4, 5-6, 12-13, 17), with the response “Have mercy on us, O Lord, for we have sinned.” This choice aligns profoundly with the day's readings: Genesis 2:7-9; 3:1-7 (the Fall and original sin), Romans 5:12-19 (sin through Adam, grace through Christ), and Matthew 4:1-11 (Jesus' temptation in the desert). The psalm echoes humanity's fall into sin while expressing hope in God's mercy and renewal, mirroring Christ's victorious resistance to temptation as the new Adam.

Its use invites the assembly to acknowledge personal and communal sinfulness at the outset of Lent, fostering humility, conversion, and trust in divine compassion as believers embark on their 40-day journey of prayer, fasting, and almsgiving towards Easter joy.