Matthew 19:13=15 The disciples must have forgotten what Jesus had said about children. Jesus wanted little children to come because He loves them and because they have the kind of attitude needed to approach God. He didn't mean that heaven is only for children, but that people need childlike attitudes of trust in God. The receptiveness of little children was a great contrast to the stubbornness of the religious leaders who let their education and sophistication stand in the way of the simple faith needed to believe in Jesus.
Matthew 19:16 To this man seeking assurance of eternal life, Jesus pointed out that salvation does not come from good works unaccompanied by love for God. The man needed a whole new starting point. Instead of adding another commandment to keep or good deeds to perform, the young man needed to submit humbly to the lordship of Christ.
Matthew 19:17 In response to the young man's question about how to have eternal life, Jesus then listed six of them, all referring to relationships with others. When the young man replied that he had kept the commandments, Jesus told him that he must do something more - sell everything and give the money to the poor. Jesus statement exposed the man's weakness. In reality, his wealth was his god, his idol, and he would not give it up. Thus he violated the first and greatest commandment.
Matthew 19:21 When Jesus told this young man that he would "be perfect" if he gave everything he had to the poor, Jesus wasn't speaking in the temporal, human sense. He was explaining ho to be justified and made whole or complete in God's sight.