Final answer:
Elie is thankful because muddy shoes mean he has avoided frostbite and other injuries related to extreme cold, which could be life-threatening, and instead signifies his ongoing struggle for survival.
Step-by-step explanation:
In the context of the passages provided, Elie is likely thankful that his shoes are covered in mud because it indicates survival. The mud on his shoes could signify that he has managed to keep moving and prevails amidst challenging conditions, such as the frost that could have caused severe damage to his feet. The emphasis on the condition of one's feet throughout the excerpts mirrors the struggle for survival in harsh conditions, where frostbite was a real danger and muddy shoes were a sign of ongoing endurance and life.