Bismillah hir Rahman nir Rahim.
And they bear your burdens, your baggage, to a land which you could not reach, without being on camel-back, save with great trouble to yourselves, [save by] straining them. Indeed your Lord is Gentle, Merciful, to you, in having created these for you.
Man is proud of his cattle and animals. As they go to, and return from, pasture, morning and evening, he has asense of his power and wealth and their beauty and docility. The animals also carry loads, and thus make inter-communication between different lands easy. But for them there would have been many difficulties, not only physical, but psychological.
Ref: Excerpts from Tafsir Ibn Kathir & The Glorious Quran: Translation by Abdullah Yousuf Ali.