Isaiah 56:6 (NET):
As for foreigners who become followers of the Lord and serve him, who love the name of the Lord and want to be his servants — all who observe the Sabbath and do not defile it, and who are faithful to my covenant —
So given that in the New Testament Paul writes that following the sabbath is a part of the shadow and the substance is found in Christ. Do we follow what Paul says about the Sabbath or do we follow Isaiah? How do we reconcile these two?