In calling Ezekiel to be a prophet, God explains Ezekiel's job as "watchman for the house of Israel." The watchman is the early warning system, the guard dog that sounds the alarm so that people can defend themselves from danger.
With the Sunday readings, the Old Testament reading is paired with the Gospel, usually to provide background or context for the Gospel. In addition to providing background, this Sunday's Old Testament reading also tells us about the importance of this Sunday's Gospel.
The job of watchman is critical, since the lives of everyone depend on the watchman's warning. If the guard dog runs away instead of barking, everyone could be in danger - this is no place for a guard dog in training. It's that important.
So why pair this with the Gospel? In addition to the message of the Old Testament reading itself, the pairing of the two readings tells us that this Gospel's message is as critical as the watchman's warning. It's that important.
More on this tomorrow.