Jamieson, Fausset and Brown on Romans 12:6-8

6-8. Having then gifts differing according to the grace given to us--Here, let it be observed, all the gifts of believers alike are viewed as communications of mere grace.

whether--we have the gift of

prophecy--that is, of inspired teaching (as in Ac 15:32). Anyone speaking with divine authority--whether with reference to the past, the present, or the future--was termed a prophet (Ex 7:1).

let us prophesy according to the proportion of faith--rather, "of our faith." Many Romish expositors and some Protestant (as Calvin and Bengel, and, though, hesitatingly, Beza and Hodge), render this "the analogy of faith," understanding by it "the general tenor" or "rule of faith," divinely delivered to men for their guidance. But this is against the context, whose object is to show that, as all the gifts of believers are according to their respective capacity for them, they are not to be puffed up on account of them, but to use them purely for their proper ends.