جَاءَ التَّاجِرُ يَحْمِلُ مِيزَانَهُ.
The merchant arrived carrying his scale.
The imperfect verbal clause yaḥmilu mīzānahu functions as a circumstantial clause (ḥāl), describing the merchant’s state on arrival. Its implicit subject pronoun refers back to the merchant, providing the linking element. An affirmative imperfect used as ḥāl normally appears without the circumstantial wāw.
Replacing it with “jāʾa al-tājiru wa-ḥamala mīzānahu” may coordinate a second action rather than describe a single concurrent state.