حمل المشبه على المشبه به بأنه هو
To predicate the comparison term of the subject as though the subject were that very thing.
In “Zayd is like a lion,” the kāf openly mediates likeness between distinct terms. In “Zayd is a lion,” that mediation is removed and the predication becomes direct. The hearer is encouraged to picture Zayd in the identity of a lion.
This effect follows from omission of the particle, not from omission of the respect. “Zayd is a lion in courage” retains this direct predication while separately specifying the feature involved.