How do we know that salvation is fully accomplished in Christ?

The assurance of salvation being fully accomplished in Christ is rooted in His fulfillment of Old Testament prophecies regarding the Messiah. Throughout His life and ultimately His death on the cross, He enacted every scriptural promise that pointed toward Him as the Savior. When Jesus declared, 'It is finished,' it was a proclamation not only of His imminent death but also of the completion of the atonement necessary for the redemption of His people. This aligns with the doctrine that nothing further is needed from believers for salvation; it is wholly a work of Christ.