تَعْجِيلُ الْمَسَرَّةِ
Bringing a cause of happiness to the listener immediately.
الْعَفْوُ عَنْكَ صَدَرَ بِهِ الْأَمْرُ
The order for your pardon has been issued.
The expression al-‘afwu ‘anka comes first, so the listener hears the most welcome information at once. The later phrase sadara bihi al-amru supplies the detail that the order has been issued.
The purpose is not just to shorten the report but to advance the source of joy. Opening instead with a vague statement about an order would postpone the reassuring news.