Exodus 20: 8 Remember the sabbath day, to keep it holy. 9 Six days shalt thou labor, and do all thy work: 10 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: 11 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.
The Sabbath of the fourth commandment is integral and inseparable to the true worship being brought to light in the above passages. This commandment in particular, is the only one of the ten that tells us Who created us, and all things, and thus, it sets the stage for all true worship, by acknowledging that God created the heaven and the earth. Jesus Christ also set us the perfect example of true worship, by habitually attending church on the 7th day Sabbath.
And all who in our day might desire to worship God in sincerity and truth would follow His lead, as the light of present truth is shed upon their pathway. One of the reasons why the Bible is laser focused on the issue of true worship in the book of Revelation is because the introduction, and the teaching of the theory of evolution has sought to eliminate The God of heaven from His work of creation, and, wherever this is done and accepted, the Sabbath which points us to God is thrown out the window.
Worthy of note is the fact that the Sunday doctrine never points to the Creator of the heavens and the earth. It might speak loftily of Christ coming forth from the grave, and His glorious ascension, but at its core, it does not tell us Who created us, and thus, it falls far short of delineating what true worship must be.
Luke 4:15 And he taught in their synagogues, being glorified of all. 16 And he came to Nazareth, where he had been brought up: and, as his custom was, he went into the synagogue on the sabbath day, and stood up for to read.
May The Lord add His blessing to the study of His word. God bless!