For in six days the LORD made the heavens and the earth, the sea, and all that is in them, but he rested on the seventh day. Therefore the LORD blessed the Sabbath day and made it holy.

Ex. 20:11 NIV

Why do we have to remember the Shabbat?

When the Eternal spoke the ten audible words from the mount, He said that the sons and daughters of Israel must remember Shabbat to sanctify it and stop from doing any creative work. The reason is that the Eternal himself made all the creation in six days and He stopped His creative work on the seventh. The Eternal therefore, is the example to follow to remember and keep Shabbat.

All the sons and daughters of the Eternal are commanded to rest on Shabbat, which is on the seventh day of the week, no other one.

Sunday was introduced as the day of rest by the system established by Constantine based on the sun-worshipping cult. When Christianity was created this system was adopted as part of its foundation; however, the Eternal doesn't change His laws and no one can say that Sunday is Shabbat. The commandment of resting on the seventh day is current today and it will be until heaven and earth pass away (Matt. 5:17-19).