The Hebrew root 'aman means to be firm, reliable, certain — the same root that gives Hebrew the word emunah, faith or faithfulness. When something is 'aman, it is structurally sound, it holds, it can bear weight. Amen applied to a statement means: this is solid, this can be trusted, this stands. Applied to a person, the same root describes someone reliable — the 'amen God of Deuteronomy 7:9, the faithful God who keeps his covenant.
In the liturgical life of Israel, amen functioned as a congregational ratification. The Levites would pronounce a blessing or curse, and the people would say amen, entering themselves into the covenant reality the words described (Deuteronomy 27:15–26). Nehemiah 8:6 records the congregation saying amen twice, lifting their hands, bowing and worshipping. 1 Chronicles 16:36 has all the people saying amen and praising the Lord at the end of a great psalm of thanksgiving. Paul describes the same practice in early Christian worship in 1 Corinthians 14:16. The word always came after something, ratifying it.
Numbers 5:22 records the first use of amen in the Hebrew Bible as a liturgical response — the woman accused of adultery responds to the priestly oath with "Amen, amen." The doubling indicates solemn acceptance of the entire process and its consequences. Deuteronomy 27 has the most sustained use in the Old Testament: twelve curses, each followed by the congregation's amen, affirming each one. The weight of the word is clear. It is not filler. It is binding ratification.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.