Hermeneutics is not only about the deductive approach to interpreting Scripture (for example, grammar and syntax) but also the inductive approach, which is to infer the generalization from several pieces of information -- sort of connecting the dots. In other words, hermeneutics is both an art (subjective) and science (objective).
The concept of the Sabbath rest described in the Book of Hebrews is one such case where the answer is conceptual, not grammatical. Essentially, David wrote Psalm 95, which was then quoted in Hebrews 4:7. The idea is that David was already in the Promised Land when he had written Psalm 95, so when he admonishes his readers not to have hardened hearts so as to enter the Promised Land, he was not referring to the literal Promised Land (because his readers like him were already there). He was instead referring to the invisible Promised Land, which is the righteousness of the Lord that will result in life after death. David must have been referring to this invisible Promised Land because he was already in the visible Promised Land, which was the real estate conquered by Joshua centuries before David (which is the whole point of Heb 4:8).
So in the literal (visible) sense, observing the Sabbath in the Hebrew Bible was not so much an act of obedience (working!) so much as an act of receiving the rest (not working!), which is the salvation of the Lord. In other words, the geographical Promised Land was the visible salvation of the Lord, which was received by not working (God provided the power)... but in Psalm 95 King David now mentions an invisible Sabbath rest as well, which brings us to address the conceptual versus the grammatical.
For example, Jesus was accused of working on the Sabbath, yet he indicated the concept that he was in fact in the process of creating rest because the Father was "working" through him (Jn 5:16-18). That is, Jesus would provide the invisible eternal life, which would be the Sabbath "rest" of God.
Please note that there was scarce mention of the words "eternal life" in the Hebrew Bible (Dan 12:2 is one explicit exception), but New Testament writers indicate that the theme was evident and was understood in the Hebrew Bible (Tit 1:1-3). In other words, the "rest" of God (whether literal or otherwise) is something you receive by not working. In the Hebrew Bible, you received the "rest" of God (visible) by not working in the geographical Promised Land (place of rest) on specifically designated days; if you disobeyed, then you spurned both the visible rest and the invisible rest that King David mentions as also existing in the equation. This invisible rest was the righteousness of God (received by faith like the Abrahamic Covenant), which is also the basis of the New Covenant, where eternal life finally comes to bear through Jesus Christ -- that is, the "work" which his Father wrought through him. Therefore today you receive the "rest" of God (invisible) by not working -- thus the mention of "dead works" by those who insisted on working as the basis of their faith, which is contrary to this invisible Sabbath "rest" (Heb 6:1 and Heb 9:14).