The effect on Night created by Elie Wiesel’s use of prepositions is a subtle one because not all of the prepositions he uses contribute to the effect. This is because prepositions are one of the most commonly used word classes and therefore inescapable in writing. To prove the point, this answer has used six prepositions already. Prepositions are a word class that show the relationship between one person, place or thing and another or between multiple persons, places or things.
There are about 130 prepositions in the English language and they are generally classed as grammatical elements (meaning tied in with the whole semantic expression) instead of lexical elements (having independent meaning of their own), although some linguists identify some usages as lexical. It is the class of lexical prepositions Wiesel uses to create the effect in Night.
In a famous quote from Night, Wiesel writes "the little faces of the children." The preposition of in this quote is grammatical having meaning only in context of faces and children; this usage of prepositions does not develop the effect of Night. Another quote does however illustrate how prepositions do develop the novel's effect is:
Behind me, I heard the same man asking:
“Where is God now?”
And I heard a voice within me answer him:
In this quote, behind and within take on lexical value with meaning of their own and thus contribute to the effect of the novel. In this quote, Wiesel is illustrating that Eliezer isn't alone; isn't the only witness to the horror; isn't the only one affected by the sight; isn't the only one whose idea of truth is challenged or even destroyed. By saying that someone was behind him, Wiesel builds a perspective of objective witness and thus creates an effect of absolute truth as opposed to personal experience and point of view.
By saying that something within him responded as though the voices of the speaker and responder were one, Wiesel confirms the unity of the experience and creates an effect establishing universal truth. These two effects thus created by the use of prepositions is very important to Wiesel's purpose in revealing the truth about the Holocaust--he has objectified his personal experience and universalized his response to the experience: his experience is no longer one individual's personal perspective, it is a universal truth.
Another example of grammatical usage of prepositions that does not help create the effect of the story is: "We were masters of nature." Here, masters and nature carry the lexical meaning and of is grammatical with no independent meaning. Another example of lexical usage of prepositions that do indeed help create the effect of Wiesel's story is:
... a corpse gazed back at me. The look in his eyes, as they stared into mine, has never left me.
The prepositions at and into, which are usually grammatical with meaning tied to lexical content words, are here given lexical meaning portraying the impact of Eliezer's struggle to see into a mirror. The corpse-like image is important but the ownership and the direction of the gaze are more important as it looks "back at" Eliezer with a look embedded "in his eyes." The recipient of the "stare" is even more important as the corpse stared "into" Eliezer's eyes. The effect created is the indelibility of the universal experience as the "look in" the corpse's eyes "has never left" Eliezer's eyes.