Jesus Christ fulfilled the law for us. The New Testament makes it clear that keeping the sabbath is a matter of spiritual freedom through the following verses.
Colossians 2:16-17 – 16 Therefore let no one pass judgment on you in questions of food and drink, or with regard to a festival or a new moon or a Sabbath. 17 These are a shadow of the things to come, but the substance belongs to Christ.
Romans 14:5 – 5 One person esteems one day as better than another, while another esteems all days alike. Each one should be fully convinced in his own mind.
This is a pretty cut and clear case. Galatians, Romans, Hebrews and Ephesians makes it very clear that we are saved by grace through faith, and not of works of the law.
Romans 3:31 does state, however, that we uphold the law. While we can’t be saved by keeping the law, we should live in accordance with it. The law shows us our need for Christ. Also, remember, part of the sabbath law was a death penalty for those who failed to keep it ( Exodus 35:2-3 ). Jesus said the sabbath was made for man, not man for sabbath, and that Jesus Christ is Lord over the sabbath.