As the run-up to the discussion on faith, Mormon spends time on understanding the principles upon which faith is enacted. Once again, that focus is on Christ. Before Christ came to the world, prophets prophesied of His mission. The reason that Mormon focuses on the prophecies from before Christ’s time is that it was a time where there was a promise made, but as yet unfulfilled. Into that void, the expectation, without a fulfillment, that faith allowed them to proceed with the correct doctrine, to learn and repent, even prior to the time when the atonement technically initiated the ability for those actions.
Thus, Mormon models faith as acting at times when the fulfillment is not known.