How do we know that resting in Christ is vital for salvation?

Resting in Christ is central to the believer's faith because it acknowledges that our salvation is not based on our works but is entirely dependent on His completed work on the cross, as stated in Hebrews 4:10, "For he that is entered into his rest, he also hath ceased from his own works, as God did from his." This rest demonstrates our faith that Christ's sacrifice is sufficient for our salvation, and that we cannot add to it through our efforts. This principle is reiterated in Mark 2:28 where Jesus claims, "The Son of Man is Lord also of the Sabbath," affirming His authority over our spiritual rest.