The term "Beadle" as in Moshe the Beadle refers to a lower level member of the clergy.  Traditionally, a "beadle" is a lay person who was used in ceremonies.  They were not the "higher" caliber of a Rabbi or a Priest.  Yet, the beadle was involved with the church or religious house of worship activities.  In the first chapter of Night, Moshe the Beadle can be seen in this light.  He does not merit the social respect of a rabbi.  Yet, people in the village associate Moshe with religious services in the synagogue.  They also link him with the spiritual aspects of the temple and the role it occupies in Sighet.  While Moshe is a beadle, someone who is not as exalted as a more elevated position in the temple, Eliezer sees him as a guru.  Moshe is well versed in religious scripture and serves as Eliezer's spiritual mentor when no one else would.  

Through this interaction, an important aspect of the thematic narrative is revealed. Eliezer's embrace of Moshe the Beadle, a lower level religious figure and not someone who is immediately associated with the more conventional understanding of spiritual expression, represents how "truth" might not be a direct or expected path.  Eliezer learns more under Moshe than he would have under another who was more "accepted."  In the same way, Eliezer comes to profound understanding of the divine and the role of spiritual salvation by an unconventional path with his experience in the Holocaust.  Moshe becomes a thematic gateway to how truth and being in the world does not have to follow socially dictated or prescribed norms.  Moshe speaks of this himself early on in the text to Eliezer:

There are a thousand and one gates allowing entry into the orchard of mystical truth. Every human being has his own gate. He must not err and wish to enter the orchard through a gate other than his own. That would present a danger not only for the one entering but also for those who are already inside.

Moshe's role as  the lower level "beadle" helps to usher in a condition in which Elizer understands that passage into the "orchard of mystical truth" is far from direct and certain.