Church Fathers on Luke 15:6

You had learnt by what went before not to be occupied by the business of this world, not to prefer transitory things to eternal. But because the frailty of man can not keep a firm step in so slippery a world, the good Physician has shown you a remedy even after falling; the merciful Judge has not denied the hope of pardon; hence it is added, Then drew near to him all the publicans.

That is, those who collect or farm the public taxes, and who make a business of following after worldly gain.

For this was His wont, for the sake whereof He had taken upon Him the flesh, to receive sinners as the physician those that are sick. But the Pharisees, the really guilty, returned murmurs for this act of mercy, as it follows, And the Pharisees and Scribes murmured, saying, &c.