"Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it.  But small is the gate and narrow the road that leads to life, and only a few find it.  Matthew 7:13-14

At the time the disciples came to Jesus and asked, "Who is the greatest in the kingdom of heaven?"  . . . "I tell you the truth, unless you change and become like little children, you will never enter the kingdom of heaven.  Therefore, whoever humbles himself like this child is the greatest in the kingdom of heaven." Matthew 18:1-4

Verse Explaination

Matthew 7:13-14
The gate is called "narrow" because to become a Christian, there is only one way to live eternally with God and only a few decide to walk that road.  Believing in Jesus is the only way to to heaven, because he alone died for our sins and made us right before God.  Living his way may not be popular, but it is true and right.  

Matthew 18:1-4
Jesus used a child to help his self-centered disciples get the point.  We are not to be childish (like the disciples, arguing over petty issues), but rather childlike, with humble and sincere hearts.  Are you being childlike or childish?