I’m sorry, but the Sabbath is found in Rev. 14 only if we read it into the verse. In this case what is the emphasis - that God is the God of all creation; or we have to worship God on one specific day? We can wander into all kinds of biblical territory from one comment, and lose the meaning and intent of the verse if we so wish.
I’m going to plead naivety, and go back to a time when I first opened the Bible to learn. It came from the hands of Adventism; but even back then, I wondered why the Adventist church depended so much on other books written about the Bible by just one person - as I read the closing verses of Revelation for the first time -
I testify to everyone who hears the words of the prophesy of this book; if anyone adds to them, God will add to him the plagues which are written in this book; and if anyone takes away from the words of the book of this prophesy, God will take away his part from the tree of life and from the holy city, which are written in this book.
Adventism is keen on having the Bible interpret itself - unless we want it to say something else. So I will give an alternative by using the proof text method taught by Adventist Bible studies:
Rev.14 is the starting point for identifying the “GOSPEL” according to SDA interpretation: the bulls eye for this chapter is Rev.14:12 - Here is the patience of the saints who keep the commandments of God and their faith in Jesus. The first part (commandments of God) are immediately translated as the fourth commandment; and the second part - “faith in Jesus” is translated as faith “of” Jesus.
This sends us to the second part of Revelation to identify further “the saints” - Rev. 19:9ff. - “Blessed are those who are invited to the marriage supper of the Lamb…” According to Rev 19:10, 11 John bowed down to the angel who was speaking to him. The angel told John not to do that because he was to worship God, and that he, the angel, is only the messenger whose “testimony” is about Jesus, who is the object (spirit) of the prophesy.
Assuming the John of Revelation is the same John of the books 1, 2, 3 preceding Revelation, John defines what the “testimony of Jesus” in 1John 5:11 - And the testimony is this, God has given us eternal life, and this life is in His Son. He who has the Son has the life; he who does not have the Son of God does not have the life.
Just because someone lifted the words “Spirit of prophesy” from the sentence, and called some writings by that name, does not give us permission to translate the sentence to mean that all we need for salvation is to “keep the Sabbath, and follow EGW books” - with no mention of the Son of God in that process. By using “The Spirit of Prophesy” as a title, rather than the description of John’s message, we imply that, that is all that’s necessary.