The word Amen is a simplified version of the mantra Aum. Judaism, Islam and Christian prayers end with Amen. The inner meaning of Amen is
In the name of God, so be it.
The mantra Om or Aum or Amen has a purifying effect and helps the consciousness shift to a higher level.
By regularly chanting the mantra Om or Aum or Amen, it is possible to pufify the incarnated soul, thereby resulting in union with the higher soul.
Source: Excerpt from Achieving Oneness with the Higher soul: Meditations for soul realization, Master Choa Kok Sui 2005