Gregory the Great
Catena Aurea · Lukasevangelium 15
Then drew near unto him all the Publicans and sinners for to hear him. And the Pharisees and Scribes murmured, saying, This man receiveth sinners, and eateth with them. And he spake this parable unto them, saying, What man of you, having an hundred sheep, if he lose one of them, doth not leave the ninety and nine in the wilderness, and go after that which is lost, until he find it? And when he hath found it, he layeth it on his shoulders, rejoicing. And when he cometh home, he calleth together his friends and neighbours, saying unto them, Rejoice with me; for I have found my sheep which was lost. I say unto you, that likewise joy shall be in heaven over one sinner that repenteth, more than over ninety and nine just persons, which need no repentance.
(in Hom. 34.) He placed the sheep upon his shoulders, for taking man’s nature upon Him he bore our sins. But having found the sheep, he returns home; for our Shepherd having restored man, returns to his heavenly kingdom. And hence it follows, And coming he collects together his friends and neighbours, saying to them, Rejoice with me, for I have found my sheep which was lost. (1 Pet. 2:24, Isai. 53.) By His friends and neighbours He means the companies of Angels, who are His friends because they are keeping His will in their own stedfastness; they are also His neighbours, because by their own constant waiting upon Him they enjoy the brightness of His sight.