Then all the people said amen. According to Wikipedia: The word amen is a declaration of affirmation found in the Hebrew Bible and the New Testament. Common English translations of the word amen include "verily" and "truly". It can also be used colloquially to express strong agreement, as in, for instance, amen to that.
Then all the people said amen is also a title of a song by Matt Maher. If you want to hear how the song sounds, here is a link to a sample. [amen song]