A trumpet alone does not sound, there must be a person behind it for it to make a sound. Echoes cannot fly, nor die. He uses this personification to make sense of the echoes spreading across the land and the dying to show how the echoes fade as time passes. He also says "They pass out on the hill, or the field, or the river," which not even an echo can do. The last lines have the echoes and the trumpet answering the original call which personifies the speaker hearing the echo of the trumpet