But when Christ had offered for all time a single sacrifice for sins, he sat down at the right hand of God, waiting from that time until his enemies should be made a footstool for his feet. For by a single offering he has perfected for all time those who are being sanctified. Hebrews 10:12-14 ESV
Solus Christus or Christ Alone, it is the concept that the only work required for our salvation was done through Jesus’s death on the cross. There are many places throughout the New Testament that makes this point. Paul tends to put it so bluntly as to state that while we were enemies of God, Christ died for us, just read Romans 5 or Colossians 1. The Old Testament also points forward to this, while the Jews of Jesus’s day, especially the religious leaders, missed it many of the prophecies pertaining to Christ’s first coming show a need for Him to be the suffering servant. However, if I just had to pick out one book of the Bible that drives home the point of Solus Christus it would have to be Hebrews. The entire book was written to believers in Rome during a time of great persecution where many were considering leaving the faith, the author seeing the problem wrote to encourage them and illustrate that Christ is far greater than any other option.
The author spends a great amount of time comparing Jesus to the priesthood, pointing out Jesus’s superiority and how the sacrifices offered up by the Levitical priests are not sufficient to cover our sins. The problem is that the Old Testament sacrifices were not perfect sacrifices offered by a perfect priest, therefore they were flawed sacrifices. This required regular trips to the temple and frequent sacrifices to cover one’s sins.
Then Jesus came along, the perfect Lamb of God, he lived a perfect life free from sin and died on the cross serving as a sacrifice for the sins of all mankind. Not only that but in doing so he also took on the role as our High Priest to stand before God in our place acting as our advocate and interceding on our behalf, covering those who have faith with his righteousness. That is why the author of Hebrews can state that those who are being sanctified are perfected once and for all through Christ’s sacrifice, because the blood that was used to cover our imperfections was the perfect blood of Christ applied by a perfect Priest and not the blood of earthly sacrifices applied by earthly priests. It is this sacrifice that makes God’s offer of grace possible; and without grace there would be no faith, and with no faith we would have no hope for salvation. So we have now seen that we are saved by grace, through faith, because of Christ’s work on the cross.