Final answer:
The contrasting descriptions in The Great Gatsby emphasize the security wealth provides, highlighting Tom's steady societal position compared to Gatsby's less secure, military-exposed existence.
Step-by-step explanation:
The contrasting descriptions in F. Scott Fitzgerald's The Great Gatsby are used to emphasize the security that comes with wealth. Nick's reference to Gatsby as being at the mercy of government highlights the instability of military life, whereas the description of Tom Buchanan's 'wholesome bulkiness' suggests a steadfast and secure position in society, which is attributed to his wealth. These descriptions serve to accentuate the relative power and stability that each character possesses, with Gatsby's apparent greatness being overshadowed by the whims of a greater structure, and Tom's wealth offering him a solid and influential standing.