Psalm 40, known as Psalm 39 in the Septuagint and Vulgate traditions, is a profound composition within the Book of Psalms, blending thanksgiving, lament, and commitment to divine obedience. Traditionally attributed to King David, its superscription in the Hebrew Bible identifies it as "Of David. A Psalm," linking it to the royal poet's experiences of deliverance and devotion around the 10th century BCE. Biblical scholarship suggests the Psalter was compiled over centuries, with Davidic authorship debated; some view the titles as later additions or references to musical guilds, while others affirm their historical authenticity based on literary and archaeological parallels from ancient Near Eastern hymnody. The psalm likely originated in a temple liturgical context, reflecting Israel's covenantal relationship with God amid trials like persecution or illness.

The selected verses (7–11) emphasise God's preference for an "open ear" and heartfelt obedience over ritual sacrifices such as holocausts and offerings. The speaker proclaims, "Behold, I have come," affirming delight in God's will as inscribed in the "scroll of the book." This theme of voluntary submission resonates theologically, portraying a righteous individual who publicly declares God's faithfulness and salvation without concealment.

In Christian interpretation, these verses gain messianic depth, as quoted in Hebrews 10:5–7 to depict Christ's incarnation and sacrificial obedience, superseding Old Testament rites. For the Mass of the Annunciation of the Lord on 25 March, Psalm 40 serves as the responsorial psalm, with the refrain "Here I am, Lord; I come to do your will" (from verses 8a, 9a). This solemnity commemorates the angel Gabriel's announcement to Mary and her fiat: "Behold the handmaid of the Lord; be it done unto me according to thy word" (Luke 1:38). The psalm's emphasis on willing obedience mirrors Mary's assent, prefiguring Christ's entry into the world to fulfil the Father's plan of redemption. It underscores the Annunciation as the pivotal moment of the Incarnation, where divine will intersects human response, highlighting themes of humility, faithfulness, and the superiority of interior devotion in the liturgy. Thus, this psalm enriches the feast, inviting believers to emulate such surrender in their spiritual lives.