Psalm 40 (Psalm 39 in some numbering systems) is a Davidic psalm of thanksgiving and supplication, likely composed by King David during a period of personal distress and subsequent deliverance. Its origins trace to the ancient Israelite tradition of individual lament and praise, reflecting David's experiences as a shepherd-king facing trials—possibly enemies, illness, or spiritual anguish. The psalm blends gratitude for God's rescue ("I waited patiently for the Lord; he inclined to me and heard my cry") with a profound declaration of obedience over ritual sacrifice, emphasizing inner faithfulness.

Structurally, it shifts from praise (vv. 1-10) to plea (vv. 11-17), with verses 13-17 mirroring Psalm 70. Historically, it belongs to Book I of the Psalter (Psalms 1-41), highlighting trust amid adversity.

In Christian tradition, Psalm 40 holds profound messianic significance. The New Testament (Hebrews 10:5-10) applies verses 6-8 to Christ: "Behold, I have come to do your will, O God." This interprets Jesus' incarnation and sacrifice as fulfilling the law, prioritizing obedience over animal offerings—a theme echoing prophetic critiques (e.g., Hosea 6:6).

For the Mass on the 2nd Sunday in Ordinary Time, Year A (e.g., January 18, 2026), this responsorial psalm (Ps 40:2, 4, 7-8a, 8b-9, 10; refrain: "Here am I, Lord; I come to do your will") resonates deeply with the readings. Isaiah 49 proclaims Israel (and ultimately Christ) as a light to nations; 1 Corinthians introduces Paul's call; John 1 features John the Baptist beholding the Lamb of God. The psalm underscores vocation and willing obedience, inviting the assembly to echo Christ's surrender to God's mission of salvation.