In the section dealing with our obligation to reach out and come to the aid of our neighbour, there is a glaring discrepancy, pointed out by Meshech Chachmah, in two adjacent pesukim. The first deals with the ger toshav, a non-Jew who has sworn off avodah zarah but is not subject to all of our mitzvos. We are commanded to support him in his time of need. The pasuk ends of, "vachai imach." The next pasuk, dealing with the prohibition of charging interest, ends of, "vechei achicha imach." The message seems almost the same but the word vachai turns into vechei.
Meshech Chachmah explains the difference between these two similar terms. One might summarize it as follows: Chei is to live whereas chai is life itself. We find the word chai used with respect to HaShem, as in "Chai HaShem," because He embodies everlasting life. The word chei is used with respect to more fleeting life, such as Yoseif's use of the term "chei Par'oah."
When we support our neighbour, the ger toshav, it is far more than providing financial stability. Since he has not accepted the full burden of all mitzvos, his sole source of "everlasting life" is his connection to our community. If we do not come to his aid, he will surely stray and give up the life he had chosen. Therefore, reaching out to him is indeed providing him with everlasting life.
The second pasuk refers to achicha, your Jewish brother. He therefore already merits the "everlasting life" by virtue of his service of HaShem and acceptance of all mitzvos, a pact he surely cannot alleviate himself of under any circumstances. Therefore, our financial support, however mandatory, is simply providing superficial, physical life. And so, the word chei is used instead.