وَفَى الرَّجُلُ بِوَعْدِهِ. الْوَفَاءُ خُلُقُ الْكِرَامِ.
The man kept his promise. Fidelity is a virtue of honorable people.
The second clause supplies a general maxim after a particular action and reinforces its meaning: this is a recognizable function of tadhyīl. An inserted parenthesis, however, offers a related aside inside a main expression whose grammatical framework can remain intact without it.
رَجَعَ صَدِيقِي ـ وَاللَّهُ أَعْلَمُ ـ قَبْلَ الْمَغْرِبِ.
My friend returned—Allah knows best—before sunset.
The aside is iʿtirāḍ, not a concluding maxim. Both add material, but their position and communicative role differ.