The "Sword" of the Word of God is it that "speaks" in Hebrews, especially in chapter 4, especially as "God THUS concerning the day The Seventh Day spake: And God, the day The Seventh Day from _ALL_, _his_, _WORKS_, RESTED."
God rested from all his works IN THAT "Jesus, had, given, them (The People of God), REST".
"Rest", therein and so that, "God after these things ( of the REST that God had given his People IN JESUS CHRIST and through HIM), shall not (again) speak of ANY OTHER 'day'-OF-SALVATION(-REST or salvation-opportunity)!" ...
"... THEREFORE [ara] ...
--- because of the once-for-all fact that "Jesus, had, given, them (The People of God), REST" ---
"... a keeping of The Sabbath Day [sabbat-ISMOS] ...
"... REMAINS VALID / OBLIGATORY / IS SUSTAINED ...
"... FOR, The People of God ...
--- specifically ---
".... BECAUSE OF / IN THAT / THROUGH THAT _HE_ ...
--- Jesus Christ ---
"... HIMSELF HAVING ENTERED UNTO [eiselthohn] ...
"... _HIS_ OWN REST as God-in-his-own."
Twice it is declared, "because Jesus had given them rest ...