Answer:
They believe that the thunder is astonishing and made the land more wondrous.
Step-by-step explanation:
"Twelfth Song of Thunder" is an anonymous poem written about the Navajo people's beliefs that gives importance to the big and small things of nature. Both are creations of god and both are equally important for the sustenance of humanity.
The lines given in the question are from the first stanza of the poem where the speaker is talking of the 'voice' of thunder. It is loud and strong, but also "beautifies the land". This particular stanza gives importance to the value of the thunder. Based on this passage, the Navajo people believe that the loud thunder is astonishing and made the land more wondrous.