I can only guess at the point the author was trying to make here. Looking at the verses cited, Gal. 3:19 states that the Law was added "because of transgressions, till the seed should come to whom the promise was made". According to verse 16, this promised seed was Christ. Maybe the author meant to show that the Law entailed a specific dispensation, and Abraham lived prior to that dispensation. Reading down a little farther, a Dispensationalist would conclude that the dispensation of the Law ended when "that faith" of verse 25 came into effect. I have added a paragraph regarding these concluding verses to the Favorable Arguments section. But unless the sentence in question receives further clarification, I can't see it as being an argument either for or against dispensationalism. It's only a statement of fact. I'm not a Darbyite, but if you think it fits better in the "Opposed to Dispensationalism" section, I have no problem with that.