Matthew 18:1-14 (ESV)
Who Is the Greatest?
18:1 At that time the disciples came to Jesus, saying, “Who is the greatest in the kingdom of heaven?” 2 And calling to him a child, he put him in the midst of them 3 and said, “Truly, I say to you, unless you turn and become like children, you will never enter the kingdom of heaven. 4 Whoever humbles himself like this child is the greatest in the kingdom of heaven.
5 “Whoever receives one such child in my name receives me, 6 but whoever causes one of these little ones who believe in me to sin, it would be better for him to have a great millstone fastened around his neck and to be drowned in the depth of the sea.
Temptations to Sin
7 “Woe to the world for temptations to sin!  For it is necessary that temptations come, but woe to the one by whom the temptation comes! 8 And if your hand or your foot causes you to sin, cut it off and throw it away. It is better for you to enter life crippled or lame than with two hands or two feet to be thrown into the eternal fire. 9 And if your eye causes you to sin, tear it out and throw it away. It is better for you to enter life with one eye than with two eyes to be thrown into the hell  of fire.
The Parable of the Lost Sheep
10 “See that you do not despise one of these little ones. For I tell you that in heaven their angels always see the face of my Father who is in heaven.  12 What do you think? If a man has a hundred sheep, and one of them has gone astray, does he not leave the ninety-nine on the mountains and go in search of the one that went astray? 13 And if he finds it, truly, I say to you, he rejoices over it more than over the ninety-nine that never went astray. 14 So it is not the will of my  Father who is in heaven that one of these little ones should perish.