faith of a mustard seed

In Matthew 17:20, Jesus says:

I tell you the truth, if you have faith as small as a mustard seed, you can say to this mountain, “Move from here to there” and it will move. Nothing will be impossible for you.

This has always been a hard verse for me. My basic interpretation has always been: Either Jesus was wrong, or no one has the faith of even a mustard seed. Because I don’t see any mountains being moved.

But this passage was also recorded in the Gospel of Thomas. This version says:

If two make peace with each other in this one house, they will say to the mountain, “Move Away,” and it will move away.

What Mathew called “faith as small as a mustard seed,” Thomas calls “two making peace with each other.” It amazes me that these two phrases are used interchangeably by the early church.

(Scholars debate the exact date when the Gospel of Thomas was first recorded. Estimates vary from 40AD to 140AD. But most agree that it faithfully represents one of the early oral Christian traditions. See wikipedia for more detail.)