Therefore we ought to give the more earnest heed to the things which we have heard, lest at any time we should let them slip.
Therefore - Because Christ the Mediator of the new covenant is so far (Hebrews 1:1-14) above angels, the mediators of the old covenant.
The more earnest, х perissoteroos (G4056)] - 'more abundantly.'
Heard - spoken by God (Hebrews 1:2); and the Lord (Hebrews 2:3).
Let them slip, х pararuoomen (G3901)] - 'flow past them' (Hebrews 4:1).