In Hebrews 2:5, the Hebrews writer doesn't speak of the aion to come, but the oikoumenē to come. What does he mean by this? When Israel received the law through angels, they then marched own into their habitation. The words that Jesus spoke looked forward to a greater world with a greater city. This is the same inhabited world that Abraham looked for in Hebrews 11. To try and be justified by the Law would cause one to forfeit their claim to the world to come as some had forfeited their right to the land of Canaan by turning back to Egypt.