For the phrase “Who has believed what we have heard? And to whom has the arm of the Lord been revealed?” see John 12:38.

Note that this quote in the New Testament is not taken from the Hebrew Bible but from the Greek Septuagint (LXX) which translates into English as “Lord, who has believed our report? And to whom has the arm of the Lord been revealed?” (Translation by NETS — for the Greek version see the title’s tooltip)