D&C 84

It is in this revelation, that the Savior reveals an -

"...oath and covenant which belongeth to the priesthood."  (Doctrine and Covenants | Section 84:39)

An  oath and covenant -

"...of my Father, which he cannot break, neither can it be moved."  (Doctrine and Covenants | Section 84:40)

Which suggests to me that because it belongeth to the priesthood which -

"...is without beginning of days or end of years."  (Doctrine and Covenants | Section 84:17)

That even the Father cannot break this oath and covenant, which oath and covenant is given to -

"...whoso is faithful unto the obtaining these two priesthoods of which I have spoken, and the magnifying their calling..."  (Doctrine and Covenants | Section 84:33)

But not only those that obtain which means to me, those that are ordained to this priesthood, but -

"...also all they who receive this priesthood..."  (Doctrine and Covenants | Section 84:35)

Receive this priesthood suggests to me, those that are worthy and obedient in and receiving the blessings and instructions of this preisthood for these are they that -

"...receiveth my servants..."  (Doctrine and Covenants | Section 84:36)

The promise or oath and covenant that belongeth to the priesthood is -

"...all that my Father hath shall be given unto him."  (Doctrine and Covenants | Section 84:38)

Is there a greater oath and covenant?  Therefore it goes without saying -

"...whoso breaketh this covenant after he hath received it, and altogether turneth therefrom, shall not have forgiveness of sins in this world nor in the world to come."  (Doctrine and Covenants | Section 84:41)

I don't believe that really changes things.  It has always been given that those who do not repent and turn from God do not receive forgiveness.  So it also makes sense that -

"...wo unto all those who come not unto this priesthood..."  (Doctrine and Covenants | Section 84:42)

In other words, their blessings and progression come to an end.

Therefore -

"...I now give unto you a commandment to beware concerning yourselves, to give diligent heed to the words of eternal life.
44 For you shall live by every word that proceedeth forth from the mouth of God."  (Doctrine and Covenants | Section 84:43 - 44)