How do we know that justification and sanctification are through grace?

The Apostle Paul clearly articulates that both justification and sanctification come through grace alone, rooted in the work of Christ. In Romans 6, he reiterates that we are justified by grace through faith in Christ's sacrificial death at Calvary. Additionally, Paul's argument continues to underline that our holiness and righteousness are found solely in Christ. Essentially, to claim that one can be sanctified by the law after being justified by grace undermines the very essence of the grace of God. Therefore, the Christian is called to rest in Christ for both their justification and ongoing sanctification, affirming that grace reigns through righteousness unto eternal life.