How do we know that Jesus is the surety of a better testament?

In the context of Hebrews, Jesus is described as the surety, or guarantor, of a new and better testament because He has fulfilled the requirements that the law could not. The old testament was based on the law and failed to provide true restoration between God and humanity. However, through His death and resurrection, Jesus confirms the better promises contained in the new covenant—namely, forgiveness of sins and the promise of eternal life. The writer affirms that this testament is based on better promises (Hebrews 8:6), emphasizing that the security of our salvation rests in the unchanging nature of Christ as our High Priest and mediator.