Can you briefly explain the Bible doctrine of “resurrection of the dead,” according to Hebrews chapter 6?

Jesus is the first resurrected One.  His victory over death and the grave opens the door for us to be resurrected just like Him.  Spiritually, we have already been resurrected from death to life.  We were spiritually dead, but in receiving Christ, we were buried with Him unto death.  And then we were resurrected with Him unto life.  So, “Therefore we are buried with him by baptism into death: that like as Christ was raised up from the dead by the glory of the Father, even so we also should walk in newness of life.  For if we have been planted together in the likeness of His death, we shall be also in the likeness of His resurrection…” (Romans 6:4,5).  Read Galatians 2:20.

Then later after death, even our bodies will be resurrected, glorified, and joined to our spirits when Jesus returns, just like Jesus was joined back with His body after He descended to hell and then back up to leave the tomb after 3 days.  His body was glorified to the point that He could walk through walls and fly up to heaven, able to live for eternity.  So will we be.  (1 Thesselonians ch. 4, 1 Corinthians ch 15, ).  If we make it alive until Jesus returns, our bodies will never die, and therefore will never be resurrected.  Instead, they will be glorified as we ascend to the sky to meet Him.  Our spirits, on the other hand, have already been resurrected from spiritual death and will not need a second one.

That is the heart of the matter.