8 ¶ He that by usury and unjust gain increaseth his substance, he shall gather it for him that will pity the poor.
This is one of those verses that crosses Christians up when they try to use claim it. This was written under the Law given to Moses for the Hebrews. Under that Law it was wrong to charge interest to impoverished fellow Hebrews or foreigners on a loan.
Leviticus 25:35 And if thy brother be waxen poor, and fallen in decay with thee; then thou shalt relieve him: yea, though he be a stranger, or a sojourner; that he may live with thee. 36 Take thou no usury of him, or increase: but fear thy God; that thy brother may live with thee.
Here we see that usury is increase or profit charged on a loan, which is what we know as interest.
A stranger is a foreigner.
Exodus 22:21 Thou shalt neither vex a stranger, nor oppress him: for ye were strangers in the land of Egypt.
A stranger and a sojourner are synonymous as a person who sojourns in a place is foreign to it and just passing through, abiding only temporarily.
Genesis 23:4 I am a stranger and a sojourner with you: give me a possession of a buryingplace with you, that I may bury my dead out of my sight.
An example of a sojourner today might be a migrant worker, a foreigner or stranger from another country, or you, a sojourner on this earth, just passing through, whose home is a far country.
The Holy Spirit, in this Proverb, is saying how a person who gains wealth dishonestly and oppressively might one day see it taken from him by someone who will show mercy on the poor. It would be ironic justice if the money he took from people were used to help that same group of people impoverished by him.
This is unlikely to happen today as the ill gotten gains of a criminal would just go into the coffers of the state who would spend it quicker than you could say “Jack Spratt could eat no fat, his wife could eat no lean.” I doubt any money Bernie Madoff pays in fines will go to show pity on the poor. Its even doubtful the investors he scammed will see much money.
However, there is a principle here. If a Christian is one of those who would make a dishonest profit and charge exorbitant interest God might well take his money and give it to someone who would show mercy on the poor.