زَيْدٌ هُوَ الْقَائِمُ.
Meaning: It is Zayd who is the standing one.
Zayd is the nominative initial subject; huwa is the separating pronoun (on the common Basran analysis without an independent case position); al-qāʾimu is the nominative predicate.
The construction identifies al-qāʾimu as the predicate, not merely an adjective of Zayd. Alternative school analyses exist; this lesson follows the source’s separation reading.