Experience teaches it, to be sure, and it's an old enough piece of common sense wisdom that it got enshrined by the Torah. Subsequently it was gifted to us by Christianity, in Pharisaical form, as crystallized by the tyranny of the Pauline consensus contaminating the gospels.
For the poor shall never cease out of the land . . ..
-- Deuteronomy 15:11a
For ye have the poor always with you . . ..
-- Matthew 26:11a
For ye have the poor with you always . . ..
-- Mark 14:7a
For the poor always ye have with you . . ..
-- John 12:8a
For Paul, "poor" is what it has always been, an explicit category which is "other", and is not the essential element and mark of Christian self-definition, let alone Jewish:
only they would have us remember the poor, which very thing I was eager to do.
-- Galatians 2:10
Except Luke will have none of it.
He alone avoids the saying because it destroys the binary. Luke knows that voluntary poverty is the mark of true repentance qualifying one to be the disciple of Jesus, to be one of the few who will escape the imminently coming judgment. Luke's Jesus does not imagine a "church" which will feed and clothe the poor, let alone one which has enough substance to feed and clothe itself and "therewith be content". The choice is only binary, God or mammon.
Hence the unique Lukan witness, which takes the place occupied by "you have the poor always with you" in the other gospels:
So likewise, whosoever he be of you that forsaketh not all that he hath, he cannot be my disciple.
-- Luke 14:33
Not very commonsensical, not very Jewish, either. Moses Maimonides did not approve. And Christians today avoid talking about it like . . . well . . . the plague.
