This is to emphasize that Ignatius had an unconventional priority and was inconsistent with other people's priorities.
Explanation:
Ignatius does not have his appearance as a priority in his life, for that reason, the clothes he wears are different from those of other people, making him become someone very peculiar, different and strange. He is probably aware of people's perception of his appearance, but he doesn't care, because he has other priorities, responsibilities and concerns.
Antithesis is being used by JFK ie by turning the question around of what your country can do for you to what you can do for your country he grabs the interest of the audience by coming up with the opposite meaning.
