Jesus condemned empty phrases in prayer because they are a way of showing off in public. He taught his followers to pray with sincerity and humility, and not to pray in a way that would draw attention to themselves. In Matthew 6:5-6, Jesus says, "And when you pray, do not be like the hypocrites, for they love to pray standing in the synagogues and on the street corners to be seen by others. Truly I tell you, they have received their reward in full. But when you pray, go into your room, close the door and pray to your Father, who is unseen." Here, Jesus is teaching his followers to pray in private and not to make a public display of their prayer. Empty phrases or long prayers do not impress God, as he already knows our needs and desires. Therefore, Jesus condemned empty phrases in prayer as they are a way of showing off in public, and are not in line with the sincere and humble prayer that he taught his followers.