What makes the radiant-faces clause a deliberate contrast with the downcast-faces clause?

Supplementary Practice 28 — Comparative Rhetoric of Sūrat al-Aʿlā and Sūrat al-Ghāshiyah

• Both clauses repeat the very same group
• A parallel syntactic frame with opposite predicates
• The second simply invalidates the first
• Only a tense change creates the distinction