We know Jesus' sacrifice is sufficient because it is described as having perfected everyone who is sanctified once for all (Hebrews 10:14).
The sufficiency of Jesus' sacrifice is affirmed in scripture, particularly in Hebrews 10:14, which states that by one offering, He has perfected for all time those who are being sanctified. This perfection signifies a complete and permanent removal of the guilt of sin for believers. Unlike the many sacrifices of the Old Testament, which were insufficient to take away sins, Christ's single offering holds infinite merit and is entirely effective for both justification and sanctification of His people. The efficacy of His sacrifice assures believers of their eternal security and unbreakable union with Him.
Commentary