Iron tools—like knives or swords—are made sharper and more useful by rubbing them against another instrument of iron. A file is similar to a blade because it is made of the same metal. But it is shaped differently.
So it is with believers. We need to interact with those who are made of the same stuff as us—who are similar to us and yet different in some ways. When we interact with each other—through conversations, shared experiences, and problems encountered—we gain knowledge, give and receive grace, and become more compassionate.
The process may generate friction at times, but it will sharpen us and make us more useful.