"In Jesus Name, Amen."
For some of us, these are the magic words that make a prayer a prayer. (If you're already offended by me calling these "magic words," then you'll quite like the rest.)
The idea of using this phrase comes from John 15:16; 16:23. Jesus says if we ask anything in his name, the Father will give it to us. Therefore, we assume that by saying the name "Jesus" at the end of the prayer, God has to respond.
We even take this one step further. The Bible makes it very clear that the name of Jesus has great power. This is partially based on Philippians 2:10 "at the name of Jesus every knee should bow, in heaven and on earth and under the earth." Therefore, we repeatedly will say the five-letter word J-E-S-U-S, believing that that combination of letters has special spiritual power.
So what is wrong with that practice?
First, we must recognize that in most cultures throughout most of the history of the world, a name was more than just what you were called. A name is a reputation or who a person really is. Think of the idea of "protecting the family name." You're not worried about how your family name is spelled, but what people think of your family.
Likewise, when we pray in the name of Jesus, it has little to do with that particular five-letter word, and everything to do with who Jesus is. In other words, Jesus commands us to pray in him.
Pray for the things he would pray for. Pray with the faith that he can deliver on his promises.
Just saying "Jesus" to make your prayer official is very literally using the Lord's name in a vain, meaningless way. Thus, by trying to obey, sometimes we do the opposite of what he has commanded.
So, pray in the name of Jesus and believe in the power of his name. But don't think that by merely saying his name you have any authority. Instead, pray in Jesus himself. Honor his reputation. Bring glory to him by the nature of your requests. That's praying in Jesus' name.
(P.S. If you don't understand the title, click on it to go to an article explaining it.)