Cursed is he who dishonors his father or mother. And all the people shall say Amein. Deuteronomy/Devarim 27:16
The Hebrew word amen, in Ashkenazi Hebrew pronounced uh-main, comes from the root emunah, faith, related to the word emet meaning truth. When we hear another reciting a blessing we respond with amen affirming that we believe what has been said. Amen occurs thirteen times in the Torah.
One rabbinic saying gives double credit to the one responding amen because to hear is akin to pronouncing. Another states that amen should not be recited in a louder voice than the one who recites the benediction because this might imply an attempt to upstage the original blessing. Another states that that all the gates of heaven open to one who recites amen and particularly it earns a child a place in the World to Come.