زَيْدٌ شُجَاعٌ
Zayd is brave.
كُنْ شُجَاعًا
Be brave.
زَيْدٌ كَالْأَسَدِ
Zayd is like a lion.
The first is an assertion assessable for truth. The second is an imperative asking for a quality. The third is an assertion that also contains a simile, making bravery vivid through a culturally familiar characteristic of the lion.
Statement versus request and presence of imagery are independent classifications. A sentence can be declarative and still contain a simile.