سَعْدٌ فِي دَارِكَ
Saʿd is in your house.
وَالسَّفَّاحُ فِي دَارِ صَدِيقِكَ
And al-Saffāḥ is in your friend's house.
The discussion uses «Saʿd», suggestive of felicity, to illustrate favorable anticipation, and «al-Saffāḥ», suggestive of violence, to illustrate the quick arrival of an unwelcome thought. The rhetorical interest is not a claim about the factual character of the named people.
Fronted expressionEffect
سَعْدٌEarly pleasant expectation
السَّفَّاحُEarly sense of concern or alarm