The phrase "the New Covenant in Jesus' blood" originates from the Last Supper, a significant event in Christian tradition described in the New Testament, particularly in the Gospels of Matthew, Mark, and Luke. Luke 22:20 records Jesus' words during this event:

"In the same way, after the supper he took the cup, saying, 'This cup is the new covenant in my blood, which is poured out for you.'"

This statement by Jesus signifies the establishment of the New Covenant through his impending sacrificial death. Here's what this phrase signifies in Christian theology:

1. New Covenant: Jesus presents the cup of wine as a symbol of the New Covenant. This New Covenant represents a new agreement between God and humanity, fulfilled and inaugurated through Jesus Christ. It's a covenant of grace, forgiveness, and reconciliation, as opposed to the covenant established with the Israelites under Moses.
2. In My Blood: Jesus refers to his imminent sacrifice on the cross, where his blood will be shed for the forgiveness of sins. His blood symbolizes the atoning sacrifice that brings about the forgiveness of sins and the restoration of the broken relationship between humanity and God.
3. Poured Out for You: Jesus emphasizes the personal nature of his sacrifice. His death is not only a historical event but also a deeply personal act of love and redemption for each individual. It's an act of selflessness, offering his life for the salvation of all who would believe in him.

This statement underscores the central Christian belief in the significance of Jesus' sacrificial death as the pivotal moment in human history, bringing about the forgiveness of sins and the establishment of a new relationship between God and humanity under the New Covenant.