What is the key function of bi-ḥamd in fa-sabbiḥ bi-ḥamdi rabbika?

Supplementary Practice 22: Comparative Rhetorical Study of Sūrat al-Kāfirūn and al-Naṣr

• Negating the imperative entirely
• Joining glorification with praise
• Turning rabbika into a past verb
• Proving that ḥamd and tasbīḥ are always synonyms