“Then someone came to him and said, ‘Teacher, what good must I do to have eternal life?’ And he said to him, ‘Why do you ask me about what is good? There is only one who is good. If you wish to enter into life, keep the commandments.’”
Now, this question could be one of anthropology, where one may think Jesus is saying that God is good, everything else (like any human being) is not. This would fly in the face of the words spoken by God after each day of creation. “He saw that it was good,” and in fact, after the creation of man in His image and likeness, “He saw that it was very good.”
The question is rather one of morality, and of the only true kind of morality: that which has it’s foundation in metaphysics – in what is real.
I will not answer very much on the morality piece itself, even though this is obviously the primary context when the text is read within the story as a whole between the rich young man and Jesus. I would direct you you to Blessed John Paul II’s encyclical Veritatis Splendor, which is fundamentally a long meditation on the depth of this very passage. I claim no ability to offer a reflection comparable to this.
I offer here, rather, a brief look at the reality itself; the metaphysical background. Jesus said “There is only one who is good.” He may just as well have said “There is only one who Is.” For God answered Moses “I am Who am.” God alone “is.” He is not created, He is not contingent, He is not changing or becoming. He is.
Jesus, if I may say so, is making the point that “what we must do” is based on “what is” (or rather, Who is). No stronger claim to objective morality vs a subjective one could be made.
All that begins, all that is contingent, has a cause, and in last analysis a supreme cause, an uncaused cause. All beings by participation depend on the Being (He that IS) by essence as on their supreme cause. That which is being by participation is not its own existence, since we must distinguish the subject which participates from the existence which it receives and participates. The rich young man (and all of us) is not his own existence, but has his existence, received from Him who alone can say “I am He who is, I am existence itself.”
God is existence itself. He does not have existence. We “have” existence, and this is because He who is existence has gratuitously shared it with us. Likewise, if we are to do what we were created to, to be what we were created to be, then this all must be based off of what “is.” This is God. “No one is good but God alone” because, in reality, “No one IS but God alone.”
Just as God created us, and therefore we “are” (but contingent upon Him), God is good, and we “are good” only in as much as we are in conformity to Him. This is the basis for all morality, and this is why Jesus says it first in the reply to what we must do.
Let us simply confirm that this is Jesus meaning, and not that we are somehow “snow covered dung-hills” or our works are just “dirty rags” by listening to the beloved disciple John:
“Dear children, do not let anyone lead you astray. He who does what is right is righteous, just as he is righteous.” 1John 3:7