It is found singly and sometimes doubly at the end of prayers (Ps. 41:13; 72:19; 89:52), to confirm the words and invoke the fulfilment of them. It is used in token of being bound by an oath (Num. 5:22; Deut. 27:15-26; Neh. 5:13; 8:6; 1 Chr. 16:36). In the primitive churches it was common for the general audience to say "Amen" at the close of the prayer (1 Cor. 14:16).
The promises of God are Amen; i.e., they are all true and sure (2 Cor. 1:20).