إِنَّ الْعُمَّالَ ـ وَهُمْ، وَالْحَمْدُ لِلَّهِ، آمِنُونَ ـ سَيُتِمُّونَ الْعَمَلَ.
The workers—who are, praise be to God, safe—will certainly finish the work.
Wa-l-ḥamdu lillāh is an inserted expression of praise. Removing it leaves the main predication, inna al-ʿummāla ... sayutimūna al-ʿamala, intact; wa-hum āminūn still supplies a description of the workers' condition. The two insertions have different functions: independent praise and a circumstantial report.
An expression is not parenthetical simply because it sits in the middle of another. Its syntactic position, relation to the subject and rhetorical purpose must all be considered.