The Reason why God established the Sabbath and why He is specifically interested in the Seventh has been made clear by God Himself, over and over again! We Rest because He Rested on the Seventh Day after Creation. This way, the memory of God as the Creator of Heaven and Earth is kept alive. We are not to REST because of RESURRECTION! Christ only left two memorials of RESURRECTION: and that is Baptism and Holy Communion. Stop defending what simply can't be defended for Sunday worship has its origin in Paganism during the Dark Ages (321 AD by Emperor Constantine) when Sunday the "Venerable day of the Sun" was officially and forcefully heaped upon the Christian world by law and with a penalty of death. This union of Church and State, Christianity and Paganism resulted into the Papacy acquiring power to enforce all the pagan doctrines then. Anyway, I digress, "We ought to obey God rather than men." Acts 5:29.
By the time the Sabbath is still Valid in the New Heaven and New Earth, you would better keep it now and not ignore this light or even worse even teach others likewise.

"For as the new heavens and the new earth, which I will make, shall remain before me, saith the LORD, so shall your seed and your name remain.
And it shall come to pass, that from one new moon to another, and from one sabbath to another, shall all flesh come to worship before me, saith the LORD." Isaiah 66:22-23.

"And it is easier for heaven and earth to pass, than one tittle of the law to fail." Luke 16:17

"My covenant will I not break, nor alter the thing that is gone out of my lips." Psalms 89:34.

"Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven."
Matthew 5:19

REMEMBER IT'S NOT A SUGGESTION!
"Remember the sabbath day, to keep it holy.
Six days shalt thou labour, and do all thy work:
But the seventh day is the sabbath of the LORD thy God: in it thou shalt not do any work, thou, nor thy son, nor thy daughter, thy manservant, nor thy maidservant, nor thy cattle, nor thy stranger that is within thy gates:
For in six days the LORD made heaven and earth, the sea, and all that in them is, and rested the seventh day: wherefore the LORD blessed the sabbath day, and hallowed it."
Exodus 20:8-11

"Howbeit in vain do they worship me, teaching for doctrines the commandments of men.
For laying aside the commandment of God, ye hold the tradition of men, as the washing of pots and cups: and many other such like things ye do.
And he said unto them, Full well ye reject the commandment of God, that ye may keep your own tradition." Mark 7:7-9.