"If you lend money to My people, to the poor among you, do not act toward them as a creditor; exact no interest from them". This comes as a warning, in case you might not wish to give to a person as a gift and be content with giving only a loan. This is actually (appropriate) for the rest of the people – those who are wealthy and well-off, but concerning the poor person, do not remain content with giving the chance gift when they happen to come by. They should always eat at your table, as the Tannah (Mishnaic sage) said, "…may the poor be members of your household".
This is why "If you lend money" is written; it means to say that if you seek to be content with giving a loan, that is for "My people" – the wealthy and the well-off. But a loan is not sufficient for the poor person – they are to be among you when eating, with you when drinking. And should it happen that the poor always eat and drink with a person, and that with time they begin to act in trickery so that the poor person understand on their own and leave; or begin to ignore them at mealtimes, and from time to time act forgetfully and not call them to share bread, so that they understand on their own and leave; or trick the borrower by pretending that they need to receive interest from them while they really must not, so that the poor individuals conclude that they are short of money and leave them on their own...
That is why concerning the first case, it says "do not act towards them as a creditor" – don't pretend to forget to eat and, concerning the second case, it says, "exact no interest from them": Do not take interest that you do not need, just to make them understand on their own and leave.