Also, what do you think he is saying, exactly?
This is an allusion to Jeremiah 50:6 and therefore a reference to the Jews. Jeremiah speaks of them as 'lost sheep' because they were 'lost' in Babylon:
Jeremiah 50:6: My people hath been lost sheep: their shepherds have caused them to go astray, they have turned them away on the mountains: they have gone from mountain to hill, they have forgotten their restingplace.
Jeremiah 50:5 says they shall ask the way to Zion (Jerusalem).
Now, in Matthew chapter 15, when the Canaanite woman asked for help for her daughter, the disciples said to send her away because she was not a Jew, but Jesus said that he was sent not just to help Jews:
Matthew 15:22-24: And, behold, a woman of Canaan came out of the same coasts, and cried unto him, saying, Have mercy on me, O Lord, thou Son of David; my daughter is grievously vexed with a devil. But he answered her not a word. And his disciples came and besought him, saying, Send her away; for she crieth after us. But he answered and said, I am not sent but unto the lost sheep of the house of Israel.
This is a reversal of the original passage in Mark 6:25-29, where Jesus implied that his miracles were like bread for the children of Israel, and not for the gentiles ('dogs') but then relented when the woman showed faith:
Mark 7:25-29: For a certain woman, whose young daughter had an unclean spirit, heard of him, and came and fell at his feet: The woman was a Greek, a Syrophenician by nation; and she besought him that he would cast forth the devil out of her daughter. But Jesus said unto her, Let the children first be filled: for it is not meet to take the children's bread, and to cast it unto the dogs. And she answered and said unto him, Yes, Lord: yet the dogs under the table eat of the children's crumbs. And he said unto her, For this saying go thy way; the devil is gone out of thy daughter.