Growing up, I remember being under the impression that in order for a prayer to "count" or to be "heard by God," one had to say "Amen" at the end of the prayer. I had no idea what this word meant, but I knew that it was necessary to close out your prayer. Indeed, no one in church, even to this day, prays without saying "Amen" at the end. I always understood the necessity of Amen having been commanded by Jesus in the Lord's Prayer.
This prayer is found in Matthew 6 and Luke 11. In these chapters, Jesus is teaching his disciples about how to pray. He commands them first not to pray in public, or with flowery speech like the hypocrites do, but to pray in secret. He then goes on to say:
"When you pray, pray like this: Our father, who is in heaven, hallowed be your name. Your kingdom come, your will be done, on earth as it is in heaven. Give us this day our daily bread, and forgive us our debts as we forgive our debtors. And lead us not into temptation, but deliver us from evil."
In Luke's version, that's where the prayer ends. But in Matthew's version, we find an additional statement at the end of the prayer..."For yours is the kingdom, and the power, and the glory forever, Amen."
Curiously enough, I recently discovered, by the footnote in the biblical text, that this phrase is not found in the earliest manuscripts of Matthew. Like so many other things in the Gospels, it was a later addition to the text. So that, coupled with the fact that the phrase doesn't appear at all in Luke's account, is a strong implication that it wasn't part of Jesus's original teaching. Thus, Jesus never taught his followers to give the now customary laudatory homily at the end of their prayers, nor to say "Amen."
This may not seem terribly important, and indeed it's probably not. But for someone who grew up with the concept that prayers literally weren't valid unless they had "Amen" at the end (a belief born entirely from Jesus's commandment on how to pray in the Lord's Prayer), this discovery really had an impact on me.
So much of what we take at face value regarding the bible isn't even historically reliable. We assume the bible is the inspired, unedited, infallible Word of God. We make this assumption because it serves our emotional needs. But what we want to be true is not always the same as what is true. The fact is, the bible has been edited, re-edited, transcribed, and re-transcribed a thousand times. Things have been added, taken away, and altered. Anyone who abides by a Christian philosophy that does not take these facts into account, is guilty of shallow faith at best, and willful idolatry at worst.