أَصْلَحَ الْعُمَّالُ أَمْرًا عَظِيمًا: فَتَحُوا الطَّرِيقَ لِلْمُسَافِرِينَ.
The workers accomplished something important: they reopened the road for travelers.
The expression amran ʿaẓīman first creates an expectation; the next clause specifies what that important achievement was. The addition is not a gratuitous second report: it answers the question invited by the initial generality.
Clarification after an initially indeterminate statement is effective when the initial vagueness directs attention to a significant later detail. If the detail is already perfectly plain and the later wording adds no benefit, repeating it is not automatically a commendable form of amplification.