Was the epistle to the Hebrews written to the Jews?

Would you agree that Hebrews is written to the Jews about a more perfect way and that the referenced scripture warns them of rejecting the Messiah that they were seeking?

The scripture referenced in the question is Hebrews 6:4-6

"For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost, And have tasted the good word of God, and the powers of the world to come, If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.

During the time that the New Testament books were written, almost all believers were Jews. Even the majority of believers in Asia minor and Rome were Jews - part of the diaspora. So the short answer is, 'yes'.

A good example of an exception might be the Corinthian church, which was probably made up mostly of Greeks.

That said, the book of Hebrews was not accidentally named. And the term Hebrew was not just a term for Jews at the time, but was typically used to designate one whose parents were both Hebrew, as Paul describes himself as a "Hebrew of the Hebrews." This would imply but not necessarily dictate that they were more devout or traditional in their beliefs that a Jew of mixed extraction.

The arguments that are laid out in this book are primarily aimed at showing that Christ, [the Messiah] is better than the old system of laws, priests and sacrifices.

It was written to warn new believers not to fall back under the law, but remain under grace.

This was also applicable to Greeks though, since the so-called "Judiazers" were constantly advising new Greek Christians that they needed to follow the law after accepting Christ.

So, it had a primary and a secondary purpose, which were closely related to following the law after accepting Christ.

And, it is also applicable to us today, as believers continue to try to obey a system of rules and regulations rather than concentrate on building a relationship with Christ through the Spirit's help to ultimately live the sanctified life.