I guess you never heard of the New Covenant? Joshua kept the Sabbath as they were under the Mosaic Covenant.
Church=ekklessia=called out one.
Assembly=synogogue= assembly.
Church is not biblical? Look it up in the Greek.
Heb 3&4 not referring to our rest in Jesus?
For we are made partakers of Christ, if we hold the beginning of our confidence stedfast unto the end;
(Heb 3:14)
Let us therefore fear, lest, a promise being left us of entering into his rest, any of you should seem to come short of it. For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it. For we which have believed do enter into rest, as he said, As I have sworn in my wrath, if they shall enter into my rest: although the works were finished from the foundation of the world.
(Heb 4:1-3)
It was not the same Gospel, it was the same God, who justified the same way...by faith.
Here is the Gospel by which if believed we enter His rest (and cease from our works of merit)
Moreover, brethren, I declare unto you the gospel which I preached unto you, which also ye have received, and wherein ye stand; By which also ye are saved, if ye keep in memory what I preached unto you, unless ye have believed in vain. For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures:
(1Co 15:1-4)