It is interesting that immediately after a discussion about the need for faith (Matt 17:14-20), we see Jesus explain his impending death and resurrection (17:22-23). Perhaps this clues us into what is the source for our faith as Christians: it is found in Jesus himself.
How do we muster up more faith in Christ? How do we more faithfully walk by faith? The answer is not by our own strength or cleverness or will-power. The answer is Christ himself. He is the “author and perfecter of our faith” (Heb 12:1-2).
In Matt 17:22-23 we see Jesus predict his death and resurrection. Jesus foretold an amazing future event was going to take place, an event which would secure our salvation through the defeating of our sin and death. Before Jesus died, he knew that he would die and he plainly told the disciples about it on multiple occasions. Though they did not get it most of the time (Matt 17:23b), they did hear the words and after Jesus did die and rise again, the words were a powerful testimony to the faithfulness of God and truthfulness of Jesus. Now, they, and we, can look back and see how faithful God is in securing our salvation and how faithful Jesus was to accomplish it.
As ponder we ponder this and let it sink into our souls, we behold the faithfulness of God. He is faithful to secure our salvation! Even when we doubt, He remains faithful. Even when we forget, He remains faithful. And, surely if He was faithful in this way, we can trust Him with other things (Rom 8:32)!
Thus, beholding the gospel strengthens us and help us to keep walking by faith. It is the fuel for our faith. It makes us strong when we are weak, it spurs us forward when we are languishing.
It is also a source of comfort for as we consider our own faithlessness. At the cross Jesus died for all our sin, including our sin of unbelief. All of our cynical doubt in God was dealt with by Jesus at the cross. All of our questioning of God’s character was put away by Jesus. All of our proud and foolish questioning of God’s kindness was dealt with by Jesus at the cross and shown to be truly foolish.
Jesus is the source of our continued faith.