Psalms 40:6
Sacrifice and offering thou didst not desire; mine ears hast thou opened: burnt offering and sin offering hast thou not required. Sacrifice and offering thou didst not desire; mine ears hast thou opened: burnt offering and sin offering hast thou not required.
The verse records Christ speaking from God's throne to announce His coming to do God's will with God's law in His heart. The rejection of sacrifice and offering in the verse belongs to that announcement of Christ's coming. The announcement was made after Adam's fall, when Christ declared His willing purpose to become humanity's substitute and surety. The same speaking occurred nearly two thousand years ago as Christ came to earth as the Light of the world.
The rejection of sacrifice and offering, including animal sacrifices and burnt offering and sin offering, means God did not desire them as an end in themselves, as the purpose He sought, as a substitute for obedience, or as the answer to sin. Instead God prepared a human body for Christ, in which Christ comes in fulfillment of what was written of Him to delight to do God's will. Christ's coming as a human being, even as a poor human being, was planned in counsel with the Father as a deliberate choice, not an accidental or chance event, and His life fulfilled that purpose.
God's law is unchangeable and cannot be altered to fit fallen humanity, so God's requirement of perfect obedience remains unchanged; Christ did not come to abolish the law but to fulfill and uphold it. To meet that requirement Christ took human nature, became human and bore the sins of the fallen race, so that His obedience provides the flawless righteousness sinners need and people may receive and become God's righteousness in Him. Christ's self-offering fulfilled the types and shadows and identifies Him as the one who alone could redeem the world.