Hold on tight

The book of Hebrews were written to the Jewish believers in Jesus. Jesus was the fulfillment of the Old Testament law.
Jesus is the great high priest from the order of  Melchizedek and that is higher than the Levi priesthood.
Since, Jesus is the Messiah, he lived a perfect life because only God is perfect. You can gather this information in Psalm 110, if you want extra credit.
He became the perfect sacrifice for mankind. The animal sacrifices were like using a credit card to pay for a item, it would pay for the item but there is still debt.
Jesus death on the the cross and the resurrection brought victory over sins. Jesus came back to life and then he went back to heaven.
Jesus conquered the power of sin and death. The issues of life always goes back to sin and death but Jesus has overcame these issues, so the Jews can be made right before God the Father.
I have good news that non-Jews can be made right before the Lord, too.

Hebrews 4:14

  Therefore, since we have a great high priest who has ascended into heaven, Jesus the Son of God, let us hold firmly to the faith we profess.