In Hebrews 3:18-19, they did not enter into God's rest because of their unbelief/disobedience, and in Exodus 20:13, it specifically mentions that they greatly profaned God's Sabbaths. In Hebrews 4:9-11, there remains a Sabbath rest for the people of God, we should rest from our work as God rested from His, and we should strive to enter into that rest so that no one may fall away by the same sort of disobedience, so he was not speaking in contrast with the weekly Sabbath, and you trying to use entering into God's rest to justify the same sort of disobedience is the opposite of what was being said.
You cited the wrong verse. Exodus 20:13 reads - "you shall not murder." Ezekiel 20:13 reads - Yet the house of Israel rebelled against Me in the wilderness; they did not walk in My statutes; they despised My judgments, ‘which, if a man does, he shall live by them’; and they greatly defiled My Sabbaths. (plural) Then I said I would pour out My fury on them in the wilderness, to consume them. The heart of the issue here is that their disobedience here was a manifestation of their
UNBELIEF.
How about a little context.
Hebrews 3:8-10 says, do not harden your hearts as in the rebellion, in the day of trial in the wilderness, where your fathers tested Me, tried Me, and saw My works forty years. Therefore, I was angry with that generation, and said,
'They always go astray in their heart, and they have not known My ways.' Not descriptive of genuine believers.
Verses 18-19 - And to whom did He swear that they would not enter His rest, but to those who did not obey? So, we see that they could not enter in because of
UNBELIEF.
*Jude 1:5 - Though you already know all this, I want to remind you that the Lord at one time
delivered his people (the Israelites) out of Egypt, but later destroyed those who did not believe. Did you see that?
DID NOT BELIEVE.
Hebrews 3:14 - For we
have become [past tense Greek verb, gegonamen, meaning we have become already] partakers of Christ,
(demonstrative evidence) if we hold fast the beginning of our confidence steadfast to the end. Notice that this is essentially a repeat of verse 6, in which we read: but Christ was faithful as a Son over His house -
whose house we are, (demonstrative evidence) if we hold fast our confidence and the boast of our hope firm until the end.
The wording is not - "and you will become partakers of Christ (future indicative) if you (future indicative) hold fast." It is rather -
"you have been, and now are a partaker of Christ" (demonstrative evidence) if in the future you hold fast the beginning of your confidence steadfast to the end."
Holding fast is proof of genuine conversion.
The point is that not all of these Hebrews have become partakers in Christ and the only ones in the end who will be identified as those who truly are partakers of Christ, will have been those who have held fast the beginning of their confidence steadfast to the end. Now what about those faltering Hebrews who depart from God, yet begin with loud confidence and profession of loyalty? But then later? Again,
holding fast is proof of genuine conversion.
To believe is to have faith and obedience which "follows" is works and is a "manifestation" of belief/faith. For those who did not hold fast, their disobedience was a manifestation of their
UNBELIEF.
Christians are not Israelites under the law, so defiling God's Sabbaths (including the weekly Sabbath) is not an option for the body of Christ under the new covenant. (Colossians 2:16-17) Ezekiel 20:1-13 is addressed to the
Israelites under the old covenant of law. This is what happens when you don't rightly divide the word of truth.
In regard to Hebrews 4:9-11, see -
Sabbath rest (4520) sabbatismos - Sermon Index