Κάλλιστον κόσμος, ποίημα γαρ θεού.

“The Universe is most beautiful for it is the work of God (Ο Θαλής ο Μιλήσιος / Thales of Miletus))

Parasing Information:

Κάλλιστον  is the neuter form of the superlative adjective “κάλλιστος” (kállistos), which means “most beautiful” or “best.” Because Κάλλιστον is neuter while κόσμος is masculine, the adjective is not simply agreeing with κόσμος. It is better understood substantivally or predicatively: roughly, “The most beautiful [thing] is the cosmos/universe.” 

κόσμος is a Greek noun that means “world” or “universe” in English. Grammatically, it is masculine in gender and can take different forms depending on its role in a sentence, such as nominative, accusative, genitive, etc.

ποίημα is a Greek noun that means “workmanship”, “creation”, or “poem” in English. It is neuter in gender.

γαρ  is a Greek particle used in ancient Greek and Koine Greek. It’s commonly translated as “for” or “indeed” in English. Grammatically, it serves as a conjunction or a particle that connects clauses, providing an explanation, justification, or reason for what was said before. It doesn’t inflect like nouns or verbs, so it doesn’t have different forms.

θεού is a Greek noun that means “of God” in English. Grammatically, it is in the genitive case, which typically indicates possession or relationship. In this form, it shows possession or association with the noun it modifies. In this case, “θεού” indicates possession by or association with God.