¶ Pretty much everyone has missed this one. I had the "Aha!" moment a number of years ago and figured it out. The key is that there is no verb "cometh." In fact, there is no verb at all. Rather, verse 17 is simply a continuation of verse 16, as so: ¶ "[16] But not all obey the good news, for Isaiah is saying, 'Lord! Who believes what is heard?' [17] based on faith in what is heard, and yet what is heard through the declaration of Christ/God. [18] But I am saying, did not Israel know? First Moses is saying..." ¶ Paul is quoting the first part of Isa 53:1 verbatim from the LXX, then adds to that. It is about Israel (verse 16), Israel (verse 17), Israel (verse 18), not Israel (verse 16) modern faith slogan "faith cometh by hearing" (verse 17), Israel (verse 18). ¶ Paraphrasing, to make more clear what I am getting at, ¶ "But not all obey the good news, for Isaiah says 'Lord! Who believes our message?' such that it would be as a consequence of faith in the message that comes through the declaration of Christ/God. But I am saying, didn't Israel know? First Moses said..."

¶ Edit to previous comment to correct the consequent of αρα in the apodosis: ¶ "[16] But not all obey the good news, for Isaiah is saying, 'Lord! Who believes what is heard?' [17] resulting in faith in what is heard, and yet what is heard through the declaration of Christ/God. [18] But I am saying, did not Israel know? First Moses is saying..." ¶ I cannot think of a corresponding conjunction in English -- that's the difficulty -- hence the participle and preposition. ¶ Paraphrasing (adding my own verb), ¶ "But not all obey the good news, for Isaiah says 'Lord! Who believes our message?' such that it would have as a consequence faith in the message that comes through the declaration of Christ/God. But I am saying, didn't Israel know? First Moses said..."