This gives the reader a sense of the burden that the men are bearing in carrying these things. Much attention is given to the weight and pressure the soldiers feel from what they're carrying and from external forces, such as nature.
Explanation:
"They carried the sky. The whole atmosphere...they carried gravity." But the greatest weight the men feel comes from nothing they can physically carry, but rather their emotions: "Grief, terror, love, longing these were intangibles, but the intangibles had their own mass and specific gravity, they had tangible weight.
