In traditional Protestant Christianity, faith in Jesus is what supposedly saves us. This notion goes back to Martin Luther. But was Luther mistranslating the Bible?
In some of Paul's epistles, there's a Greek phrase that is conventionally translated as "faith in Jesus." See, for example, Romans 3:21, 26 and Galatians 2:16.
Annotated Bibles often set forth an alternate translation of the Greek, namely "the faith of Jesus." The HarperCollins Study Bible [NRSV] observes, at Rom. 3:22, that "[t]he alternate translation ... is closer to the Greek and is gaining acceptance, though some prefer 'faithfulness' ...."
The alternate translation seems more consistent with Paul's overall argument that faith in God, exemplified by the faith of Jesus, is what causes us to be reckoned as righteous, as it did with Abraham (see Rom. 4:1-25).
Moreover, the alternate translation seems more consistent with Jesus's reported teachings, which centered on faith in God, not in Jesus.
See also this article for a summary of some of the different scholarly views on this point.