This verse describes the Lord as the Protector of the weak; people who do not expect anything of themselves; or people who, through circumstances they find themselves in, are looked down upon, and are no longer being counted. That had happened to the author, but the Lord saves or liberates him. That is what the ending of this verse states.
6 L'Eternel garde les simples;J'étais malheureux, et il m'a sauvé.