Jesus explains that these hypocrites pray for show. They get up in front of crowds and pray so eloquently in order that others would see them and praise them for it. They were going it about it in a wrong and sinful way. They received the reward they wanted, the praise of others, but they ignored the enjoyment of conversing with God. You can have prayers that would wow any crowd, but if your heart is not in it, you gain nothing lasting from it.
What is your motivation for prayer, and how can putting your heart in your prayers help you grow in Christ?