"When you lend money to My people..." (Shemos 22:24)
There is a mitzvah to grant loans to our fellow Jews. This mitzvah is
even greater (in a certain sense) than that of giving charity, since
through a loan one can help someone else in a more dignified manner,
without him suffering shame (Rambam, Hilchos Matnas Aniyim 10:7).
The proper attitude to have when giving charity or a loan is that Hashem
could have given the other person the mondey directly, but He desires to
give us the opportunity to do a mitzvah and thus makes us the agent to
deliver the money (Sefer HaChinuch, mitzvah 66).
One may not put pressure on the borrower to pay up is he knows that he is
unable to pay at that point. One may not eben walk by him at such a time,
since it may cause him fear or shame (Rambam, Hilchos Malveh 1:3).