A.T. Robertson Commentary Romans 12:6

"And having gifts differing according to the grace that was given to us, whether prophecy, [let us prophesy] according to the proportion of our faith;" — Romans 12:6 (ASV)

Differing (διαφορα). Old adjective from διαφερω, to differ, to vary. So Heb 9:10.

According to the proportion of our faith (κατα την αναλογιαν της πιστεως). The same use of πιστις (faith) as in verse 3 "the measure of faith." Old word. αναλογια (our word "analogy") from αναλογος (analogous, conformable, proportional). Here alone in N.T. The verb προφητευωμεν (present active volitive subjunctive, let us prophesy) must be supplied with which εχοντες agrees. The context calls for the subjective meaning of "faith" rather than the objective and outward standard though πιστις does occur in that sense (Galatians 1:23; Galatians 3:23).