The Sabbath is as old as Earth itself

Was founded at the foundation of the Earth

When the foundations of the earth were laid, then was also laid the foundation of the Sabbath. I was shown that if the true Sabbath had been kept, there would never have been an infidel or an atheist. The observance of the Sabbath would have preserved the world from idolatry. {LS 96.1}

I was shown that the law of God would stand fast forever, and exist in the new earth to all eternity. At the creation, when the foundations of the earth were laid, the sons of God looked with admiration upon the work of the Creator, and all the heavenly host shouted for joy. It was then that the foundation of the Sabbath was laid. At the close of the six days of creation, God rested on the seventh day from all His work which He had made; and He blessed the seventh day and sanctified it, because that in it He had rested from all His work. The Sabbath was instituted in Eden before the fall, and was observed by Adam and Eve, and all the heavenly host. God rested on the seventh day, and blessed and hallowed it. I saw that the Sabbath never will be done away; but that the redeemed saints, and all the angelic host, will observe it in honor of the great Creator to all eternity. {EW 217.2}

… that the God who made the heavens and the earth is the only true and living God, the author of Christianity, the author of all truth, who instituted the seventh-day Sabbath when the foundations of the world were laid, when the morning stars sang together, and all the sons of God shouted together for joy. All nature will bear testimony, as designed, for the illustration of the word of God. {FE 374.1}

It is as old as the world itself

Many urged that Sundaykeeping had been an established doctrine and a widespread custom of the church for many centuries. Against this argument it was shown that the Sabbath and its observance were more ancient and widespread, even as old as the world itself, and bearing the sanction both of angels and of God. When the foundations of the earth were laid, when the morning stars sang together, and all the sons of God shouted for joy, then was laid the foundation of the Sabbath. Job 38:6, 7; Genesis 2:1-3. Well may this institution demand our reverence; it was ordained by no human authority and rests upon no human traditions; it was established by the Ancient of Days and commanded by His eternal word. {GC 454.3}

It is intended to convey a specific message

And the Holy Spirit through the prophet Isaiah declares: “To whom then will ye liken God? or what likeness will ye compare unto Him? . . . Have ye not known? have ye not heard? hath it not been told you from the beginning? have ye not understood from the foundations of the earth? It is He that sitteth upon the circle of the earth, and the inhabitants thereof are as grasshoppers; that stretcheth out the heavens as a curtain, and spreadeth them out as a tent to dwell in. . . . To whom then will ye liken Me, or shall I be equal? saith the Holy One. Lift up your eyes on high, and behold who hath created these things, that bringeth out their host by number: He calleth them all by names by the greatness of His might, for that He is strong in power; not one faileth. Why sayest thou, O Jacob, and speakest, O Israel, My way is hid from the Lord, and my judgment is passed over from my God? Hast thou not known? hast thou not heard, that the everlasting God, the Lord, the Creator of the ends of the earth, fainteth not, neither is weary? . . . He giveth power to the faint; and to them that have no might He increaseth strength.” “Fear thou not; for I am with thee: be not dismayed; for I am thy God: I will strengthen thee; yea, I will help thee; yea, I will uphold thee with the right hand of My righteousness.” “Look unto Me, and be ye saved, all the ends of the earth: for I am God, and there is none else.” This is the message written in nature, which the Sabbath is appointed to keep in memory. When the Lord bade Israel hallow His Sabbaths, He said, “They shall be a sign between Me and you, that ye may know that I am Jehovah your God.” Isaiah 40:18-29; 41:10; 45:22; Ezekiel 20:20, R. V. {DA 282.2}