How do we know that the Old Covenant is not applicable to New Covenant believers?

The fulfillment of the Old Covenant in Christ is pivotal to understanding its applicability. Key New Testament passages such as 2 Corinthians 3, Galatians 3 & 4, and Colossians 2 affirm that the law-covenant has ended. The Sabbath, which was integral to the Old Covenant, is no longer a requirement for believers. Instead, believers find their rest in Jesus, who embodies the true Sabbath, as indicated in Hebrews 4:9-10. The emphasis on legalistic observance of days or rituals contradicts the grace that defines the New Covenant.