Ephesians 2:8, why is "πίστις" in the Genitive?

Question

Sorry if this seems like a dumb question but I am not well versed with N.T. Greek Grammar, but I am decently versed with Germanic grammar, which is probably too different in some cases to be sufficient alone.

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I was preparing a response on my opinions that faith and grace do not save us, but Jesus saves by using grace which is come by grace, because of my understanding of how my Bible translates the sentence as: "For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: not of works, lest any man should boast."

I rewrite that verse, as I understand it, as: "So (Jesus) via grace saved y'all, via faith, and that (salvation) not of yourselves; it's the gift of God: not from works, lest any person should boast."

Seeing that τῆς πίστεως is used and not τῇ πῐ́στει nor τὴν πῐ́στῐν makes me wonder why the verse is not translated somewhere along the lines of: "... through faith's grace are you all saved... " But again, that is with my proud understanding of germanic grammar, and I know full well not all languages use the same declensions for the same purposes-- to my understanding, modern Greek uses accusative similar to English's variant of oblique case.

I do believe that I read on two occasions that in one, genitive case is used in Hebrew and therefore in biblical greek to fulfill the dative, and in another that because Ancient Greek had no specific instrumental case, genitive, dative, and accusative were used by various peoples to fulfill the ablative.

I guess that that would make sense, not all dialects use the same grammars; my dialect from English uses the oblique them as nominative those and my idiolect uses plural agreement between possessors and possessees roles.

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Thank any and all in advance.

Answer 1

The relevant Greek text is:

τῇ γὰρ χάριτί ἐστε σεσωσμένοι διὰ τῆς πίστεως, καὶ τοῦτο οὐκ ἐξ ὑμῶν· Θεοῦ τὸ δῶρον·

The preposition διὰ can take either the accusative or genitive case.

According to Blass et al., A Greek Grammar of the New Testament and Other Early Christian Literature, διὰ with the genitive can something like "by means of"; or, in the case of time, it can mean "after" (e.g. "through several years"). When used with the accusative, it refers to motion (e.g. running through something) or, in an alternate meaning, cause. It is somewhat ambiguous, then, since "because of" and "by means of" hold similar meanings.

In any case, since Ephesians 2:8 is clearly referring to agency and not time or motion, by means of faith or through faith is probably the correct translation of διὰ τῆς πίστεως.

Note that in the 1951 Schlachter translation of the text, vermittels is used to translate διὰ, coincidentally also taking the genitive case:

Denn durch die Gnade seid ihr gerettet, vermittels des Glaubens, und das nicht aus euch, Gottes Gabe ist es.