The best way to
find out is to look for usage of these words in Paul's seven deemed
“become poor” (Greek root 'ptōcheuō') is only used here in the Pauline epistles. But “poor” (Greek root 'ptōchos') appears in:
Ro 15:26 “for it pleased Macedonia and Achaia well to make a certain contribution for the poor of the saints who [are] in Jerusalem;”
2 Cor 6:10 “as sorrowful, and always rejoicing; as poor, and making many rich; as having nothing, and possessing all things.”
Gal 2:10 “only, of the poor that we should be mindful, which also I was diligent -- this very thing -- to do.”
“poverty” (Greek root 'ptōcheia') shows in:
Cor 8:2 “because
in much trial of tribulation the abundance of their joy, and their
did abound to the riches
of their liberality;”
From these quotes, we have to conclude that, for Paul, “poor” and “poverty” is relative to material/financial wealth (or rather a lack of it). In any case, it is not about any spiritual deficiencies.
Let's look now for occurrences of “rich” and “become rich” in the same epistles.
“rich” (Greek root 'plousios') is not found again but the word “riches” (Greek root 'ploutos') is in:
of His goodness, and forbearance, and long-suffering, do you
Rom 9:23 “and that He might make known the riches of His glory on vessels of kindness, that He before prepared for glory, whom also He did call -- us --”
Rom 11:12 “and if the fall of them [Jews][is] the riches of a world, and the diminution of them the riches of nations, how much more the fulness of them?”
Rom 11:33 “O depth of riches, and wisdom and knowledge of God! how unsearchable His judgments, and untraceable His ways!”
Cor 8:2 (already quoted)
rich” (Greek root 'plouteō') appears in:
Ro 10:12 “for there is no difference between Jew and Greek, for the same Lord of all [is] rich to all those calling upon Him,”
1 Cor 4:8 “Already you are having been filled, already you were rich, apart from us you did reign, and I would also you did reign, that we also with you may reign together,”
From these quotes, we have to conclude that, for Paul, “riches” and “become/be rich” is not relative to material/financial wealth, but rather to spiritual fulness, abundance, plenitude &/or gifts.
So now the question is: where did Jesus get poor?
Mythicists will have to find evidence for material/financial poverty in some lower heaven or this enigmatic world of myth (starting by demonstrating their existence in the mind of ancients!).
But, of course, if Jesus lived on earth, it's not a problem because most people there & then were poor.
Richard Carrier is adamant that "became poor" in 2 Cor 8:9 means "became poor in power", with no evidence whatsoever, except that some other mythicists postulated it (and that would make it fit into his minimal mythicism theory). See here