Expository text will focus on educating its reader. Other descriptors of exposition are clear, concise, and organized writing.
The function of the infinitive phrase in the sentence <em>To win a marathon is my goal </em>is object of the verb.
It is definitely an object, and it would follow a verb if it were a normal ordering of words in the sentence (My goal is to win a marathon), and since it is not preceded by a preposition, it cannot be object of the preposition, but of a verb.
