This parable - See the notes at Matthew 13:3.

And he spake this parable unto them,.... To the Pharisees, for their conviction and confutation; and to the publicans and sinners for their encouragement; and in vindication of himself; and not only this, but the other two, concerning the lost piece of money, and the prodigal son, which were said at this time, and on the same occasion;
saying, as follows.

I. THE LOST SHEEP. (Luke 15:3-7)
Occurring again (Matthew 18:12-14); but there to show how precious one of His sheep is to the Good Shepherd; here, to show that the shepherd, though the sheep stray never so widely, will seek it out, and when he hath found, will rejoice over it.

What man of you, having a hundred sheep? Three parables spoken in succession to show how cordially God "receiveth sinners." The shepherd who loseth one sheep out of the flock of a hundred will leave the rest and go to seek the straying one.
Layeth it on his shoulders. A common custom with Eastern shepherds.
Rejoicing. So every servant of God should rejoice at the return of a sinner.

He spake - Three parables of the same import: for the sheep, the piece of silver, and the lost son, all declare (in direct contrariety to the Pharisees and scribes) in what manner God receiveth sinners.