"In conservative Protestantism Romans 12:6 is viewed as the biblical reference for the term "analogy of the faith" (i.e., αναλογἰα τῆς πἰστεως). The Bible alone is considered the word of God and the only infallible standard for judging faith and practice;" - Rule of Faith, Wiki

I first encountered this understanding of Romans 12:6 in Allert's book and couldn't really argue with it.

But last night I read Kittel (scroll down to αναλογἰα ) and, clearly, it runs contrary.

Here's the key part:

The πίστις ("faith") which underlies this correspondence, however, is not the regula fidei of the objective content of Christian faith or the doctrine of faith. This is proved beyond dispute by the parallelism both of ἑκάστῳ ὡς ὁ θεὸς ἐμέρισεν μέτρον πίστεως ("as God has apportioned a measure of faith," v. 3) and of κατὰ τὴν χάριν τὴν δοθεῖσαν ἡμῖν ("according to the grace given to us," v. 6).

Only the believer can exercise the χάρισμα ("gift"); the power of the χάρισμα ("gift") stands in αναλογἰα ("proportion") to the power of the faith appropriate to each. This is true of all χαρίσματα ("gifts"). But in others, e.g., the healing of the sick, the correspondence is externally visible, since the power of the χάρισμα ("gift") disappears with the cessation of faith. In the case of προφητεία ("prophecy"), however, which needs other special tests of its genuieness, there is the inherent temptation to exercise it without πίστις ("faith"). The reminder is thus needed that it is truly possible only κατὰ ἀναλογίαν πίστεως ("according to the proportion of faith").

Now I need to find Allert's book and look at it again. I also wish I'd seen this sooner.