Joab, we are no longer bound by the Law, of which the 10 Commandments are a part. If we are bound by the 10 Commandments as written, then we must also be subject to the specific punishments prescribed in the OT for breaking each Commandment. Yet, we are not. Thus, we are not bound by the Commandments themselves (which are legal requirements), but by the righteousness (perfected in the Person of Christ) that lies behind each of the Commandments. And so, by selecting Sunday as its day of worship, the Church holds to the righteousness of the Commandment while being free from the Law of the Commandment itself. Further, no Christians of the early Church kept the Sabbath observance. On Saturdays, the earliest Christians lived and worshipped as Jews, evangelizing their Jewish brethren in the synagogues (a work). Their “day of rest,” the day on which they gathered to pray and worship among themselves exclusively was the following day, the Lord’s Day: Sunday.
This first site is for the late John Paul II’s encyclical,
Dies Domini (on the proper keeping of the Lord’s Day):
vatican.va/holy_father/john_paul_ii/apost_letters/documents/hf_jp-ii_apl_05071998_dies-domini_en.html
This second site specifically addresses the “Seventh-Day observers” with links to fundamental articles on the subject:
diesdomini.com/