The last day of the week commemorated a finished creation (physicality). The first day of the week commemorates a finished redemption (spirituality). Now the bible says the physical law was only a shadow of the spiritual law- which is found in Christ. (Colossians 2:16,17). What He's saying here is don't let someone who practices things such as the Sabbath day judge you, because these were a shadow of the realities to come. The reality is spirituality- not physicality. For example, if you truly love God and your neighbor, you will not in that moment murder them or steal from them. Therefore, the law can be kept through spiritual means (love) instead of physical lists (the written code).