"Who were they who heard and rebelled? Were they not all those Moses led out of Egypt? And with whom was he angry for forty years? Was it not with those who sinned, whose bodies fell in the desert? And to whom did God swear that they would never enter his rest if not to those who disobeyed? So we see that they were not able to enter, because of their unbelief." NIV translation
The rest that is spoken of, here, is different than the rest of salvation.
This rest speaks of God's provision in the world for today. As with Israel when they refused to enter the promised land, we, as Christians, can choose to doubt God's provision for all of our needs. If we do so, we (like Israel) will get a wilderness experience where we learn that God is the provider and sustainer. We can chase around looking for the blessing or we can accept what Jesus has done and is willing to do. If we are His, then, He will allow us to rest in Him and know that He is our Sustainer. If we believe and trust in Him, then, we will be blessed (not have to worry) about our food, clothes, shelter, etc.