The Gospels are always fascinating to me because the disciples get a lot of things wrong. It's clear that they're often uncertain as to the fullness of Jesus' identity. Jesus corrects them at times, and sometimes he has to explain things over and over again. You start to get the feeling that Jesus could've chosen people who might have had more precise insight into the identity of the Messiah.
But they stayed with him in his trials. For all their faults, they were faithful. They were steadfast. And here, Jesus promises them a seat at the table and a throne in the Kingdom. Not for their perfection, but for their faithfulness.
There's a lesson here for us. We don't have to be perfect. We don't have to understand everything. But stay faithful. Remain. Even when it gets hard, when the way is unclear and the road is shrouded in shadows... stay faithful. Cling to God, trusting that God is holding on to you. Stay faithful -- the Kingdom is at hand.