8 Though he were a Son, yet learned he obedience by the things which he suffered;
9 And being made perfect, he became the author of eternal salvation unto all them that obey him;
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As is clear, for Paul the 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, already in pre-Christian times, the presence of God was associated and by which it was accompanied. And since the Kingdom is permeated by this presence, it is permeated by 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, simply by observing certain norms and rules, even the most excellent ones. Human righteousness always turns out to be only a reflection of God's righteousness, and a righteous person should of course be considered not a sinless person, for there are none 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 came into the world. With goodness everything is not so unambiguous: the corresponding Greek word is fairly universal; it can denote all that is good in general that is found in the world and in human nature. But the idea of soundness and quality predominates in its semantic field, as in the Hebrew word whose equivalent it is.
It is that same "goodness" that belonged to the world at creation, when God, creating the world, looked at what He had made and saw that it was "very good," or "good exceedingly," according to the Synodal translation. It disappeared, ceased to be characteristic of the world after the fall. But in the Kingdom there is no deficiency, and everyone living its life is freed from it, first of all as regards his own human nature.
Before this was impossible for anyone, even for the righteous person; now this possibility has been 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 was before, but reality. Of course, the ideal of righteousness always existed, long before the Savior came into the world, but it 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 carries the Kingdom in Himself; through Him one can share in the Kingdom; He is the fullness of life and truth embodied, 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, for he understands that Christian life is possible only as the life of the Kingdom in all its fullness.