"For if Joshua had given them rest, God would not have spoken later about another day. There remains, then, a Sabbath-rest for the people of God; for anyone who enters God's rest also rests from his own work, just as God did from his. Let us, therefore, make every effort to enter that rest, so that no one will fall by following their example of disobedience." NIV translation
Joshua led Israel into the promised land that God had provided but they still looked to their works to give them salvation rest. They would strictly keep the Sabbath and the rest of the law but it did not have the power to bring them to a place where they could rest in the knowledge that they are saved forever.
There is much debate today about the Sabbath and keeping the Sabbath. There are those who strictly hold to the fact that Saturday was the Jewish Sabbath while many "churches" portray Sunday as the "new Sabbath". The simple fact of the matter is that, for those who are in Christ, the Sabbath-rest is every day. Every day we rest in the fact that the work of our salvation was finished when Jesus said "It is finished" while He was on the cross. We also have the rest of knowing that it is permanent and that God takes care of His children. We may not live in the land of Canaan but He still provides for the daily needs of His people.