وَأَمَّا كَوْنُهُ فِعْلًا فَلِلتَّقَيُّدِ
The predicate may be cast as a verb in order to connect the predication with one of the three temporal divisions.
A verb form can convey the occurrence of an event together with temporal orientation. A noun does not necessarily encode such an orientation in the same way.
This does not mean that the verb form always specifies an exact moment on a clock. Past and non-past expressions are further interpreted in context; additional indications may narrow the intended time.