NOTES for Heb 5:8-9
For Paul, Christian life is life in the Kingdom that the Savior brought into the world. That is why he calls Christians "sons of light": the issue is undoubtedly that light with which, even in pre-Christian times, God's presence was associated and accompanied. And since the Kingdom is permeated with this presence, it is permeated with light as well. The distinguishing marks of a person living the life of the Kingdom, according to the apostle, are goodness, righteousness, and truth. As for righteousness, no special questions arise: indeed, life in the Kingdom is unthinkable without righteousness.
This does not at all mean that one can become righteous by oneself, without God's help, merely by observing certain norms and rules, even the most remarkable ones. Human righteousness always proves to be only a reflection of God's righteousness, and of course the righteous person should be considered not a sinless person, for there simply are no such people in the world except the Savior Himself, but a person who knows how to follow God and bear witness to Him despite his own sinfulness. But all this was known even before Christ's coming into the world. With goodness everything is not so unambiguous: the corresponding Greek word is quite universal; it can denote everything good in general that is found in the world and in human nature. But in its semantic field the idea of soundness, of good quality, predominates, as in the Hebrew word whose equivalent it is.
This is the very "goodness" that belonged to the world at creation, when God, creating the world, looked at what He had made and was convinced that it was "very good," or "good exceedingly" according to the Synodal translation. It disappeared, ceased to be proper to the world after the fall. But in the Kingdom there is no deficiency, and everyone who lives its life is freed from it, first of all with respect to his own human nature.
Previously this was impossible for anyone, even for a righteous person; now this possibility has opened to everyone who has shared in the life of the Kingdom. And the fullness of life is inseparable from truth, which now becomes not speculation, as it had been before, but reality. Of course, the ideal of righteousness always existed, long before the Savior came into the world, but it also always remained unattainable.
Now the ideal has become reality. It is no accident that Jesus speaks of Himself as the way, the truth, and the life: He bears the Kingdom in Himself; through Him one can share in the Kingdom; He is the fullness of life and embodied truth, the embodied ideal of righteousness, and in union with Him every Christian can and must become such an embodied ideal of righteousness. This is what Paul calls the addressees of his letter to do: he understands that Christian life is possible only as the life of the Kingdom in all its fullness.