'Amen',... in Hebrew, is one of a cluster from a root which signifies reliability, integrity and truth.... Our utterance of it is acknowledgment of God's 'Amen', which always goes before. The recognition of God's integrity and truthfulness, unswerving faithfulness in execution of his promises, is so central to Judaism's faith that 'Amen' may almost be taken as a name for God. We might miss this when we read, in the sixty-fifth chapter of Isaiah, that 'he who takes an oath in the land shall swear by the God of truth', but the Hebrew here, if rendered literally, would be 'by the God Amen'.

Believing Three Ways in One God: A Reading of the Apostles' Creed (1992)