Why do you say amen after preying?

Do you mean, why do they repeat the Word 'amen'? I would like to know the reason for that as well. I have tried to research it online and the only answer I have found is that the repetition indicates emphasis or that what was said is very important and true. Jesus used it in the gospels at the beginning of a statement. Often it is translated as "Verily, verily..." or "Truly, truly I say to you..." But the actual Word there is "amen." There are a few Psalms I think that repeat the amen at the end. In both cases, it was said for emphasis or to stress the truth of what was said.

However, I had a pastor many years ago who always said "Amen and amen." at the end of certain prayers or statements and he explained it differently and for the life of me, I cannot remember what he said. It was something like an agreement between the parties involved. Like you were affirming your prayer before God and He (God) was affirming it back to you. But that always made me feel a little uncomfortable -- assuming something on God's behalf. Like, I say, "Amen" and then God replies, "Amen." But I am saying both of the amens for us together. That was kind of the drift of what he said, but I thought I must have misunderstood, because it seems kind of presumptuous, don't you think?

Anyway, if anyone else has ever heard anything like this, perhaps you can shed a little light for us.