خَالِدٌ أَمِينٌ. خَالِدٌ لَا يَخُونُ.
Khalid is trustworthy. Khalid does not betray a trust.
The second clause naturally reinforces the first by denying the opposite of the same quality. Compare:
أَحْسَنْتُ إِلَيْهِ. دَفَعْتُ عَنْهُ الدَّيْنَ.
I did him a favor. I paid his debt.
When the second clause identifies precisely what that favor consisted of, substitution or explanation is more prominent. Both patterns may involve faṣl, yet their rhetorical grounds differ: confirmation in the former, determination of the intended act in the latter.