Albert Barnes Commentary Matthew 18:12-14

"How think ye? if any man have a hundred sheep, and one of them be gone astray, doth he not leave the ninety and nine, and go unto the mountains, and seek that which goeth astray? And if so be that he find it, verily I say unto you, he rejoiceth over it more than over the ninety and nine which have not gone astray. Even so it is not the will of your Father who is in heaven, that one of these little ones should perish." — Matthew 18:12-14 (ASV)

To show even further the reason why we should not despise them, he introduced a parable showing the joy felt when a lost thing is found. A man rejoices more over the recovery of one of his flock that had wandered than over all that remained. So God rejoices when a person is restored, seeks their salvation, and wills that not one thus found should perish. If God thus loves and preserves the redeemed, then surely we should not despise them. (See this passage further explained in Luke 15:4-10).