Imam repeating some verses that speak of mercy or punishment

I do not know of anything wrong with that, because it encourages the people to ponder and focus and benefit. It was narrated that the Prophet (peace and blessings of Allaah be upon him) repeated the verse (interpretation of the meaning): “If You punish them, they are Your slaves, and if You forgive them, verily, You, only You, are the All‑Mighty, the All‑Wise” [al-Maa’idah 5:118] several times.  

To sum up: if it is done for a good reason and not for the purpose of showing off, then there is nothing wrong with it, but if he thinks that repeating it may annoy them or result in disturbing sounds such as weeping, then it is better not to do that, so that there will not be any distraction. But if repeating it will only lead to pondering and proper focus on the prayer, then it is all good. End quote.