I'd do a thread on that but D'ists have been whining like snowflakes about new threads. I did an essay yesterday on I Cor 15 and Heb 1-2.
Hebrews...
The world was about to end in fire. It was expected right after the destruction of Israel. It was expected that decade. To warn Jews and to get them to work as fervently as Paul in the mission of the Gospel, Hebrews tells them they are to put aside the old covenant, because Jesus is greater than angels (who delivered the Law to Moses), to Aaron, and to the old covenant. They are about to inherit the world to come (2:5) which is the 'great salvation' of 2:3. To help spread this word and the mission, the Holy Spirit has been given as so many prophetic passages said (the outpouring).
Christ has been enthroned (1:5 from Ps 2, 1:6, 1:8 from Ps 45, 1:13 from Ps 110), but we do not yet see this world subject to him--especially the people of Israel in the turbulence of their rebellion to fight for the old covenant and its theocracy. Had they listened to Christ (the Luke string of verses on the kingdom) they would know why.
Their generation matches the one between the exodus and the entry of Canaan, the 'world to come' being the new 'land' that is coming. They must feed on Christ alone, not on the 'onions' and 'watermelon' of the old covenant, and may even share Christ's disgrace of dying outside the city (13:11-14; Rev 11:8's Jerusalem as Egypt).
While it was expected to happen very soon, right after the destruction of Israel, God delayed. Christ had allowed for that by saying only the Father knows.