How do we know that Christ's death was not in vain?

Christ's statement in John 6:39 reveals the certainty of salvation for His chosen people: 'This is the Father's will which hath sent me, that of all which He hath given me I should lose nothing.' His death was not a mere attempt to save, but rather an effective means of salvation for all those the Father has given Him. This powerful assertion assures believers that rather than dying in vain, Christ’s work guarantees the redemption of every elect individual, emphasizing His successful role as Savior and the profound assurance of eternal security.