Perhaps the first reference to Israel as lost sheep is in Isaiah 53:6 where the prophet wrote, “All we like sheep have gone astray.” He was of course referring directly to the Jewish nation, although prophetically to the whole world.
Some years later, the prophet Jeremiah was more specific as he wrote by the Lord's guidance in 50:6, “My people have been lost sheep.” However, take note where the Lord lays the blame. In the next sentence He says, “Their shepherds have led them astray.”
That of course does not absolve Israel of her sin, but it does give us God's perspective. He embellishes that in Ezekiel 34:1&2, “and the word of the LORD came to me, saying,'Son of man, prophesy against the shepherds of Israel, prophesy and say to them, thus says the Lord GOD to the shepherds: Woe to the shepherds of Israel . . .''’
Later in Ezekiel 34, verse 23, God explains part of His plan for restoration. He says, “I will establish one shepherd over them, and he shall feed them - my servant David. He shall feed them and be their shepherd.” King David had breathed his last hundreds of years earlier, so this statement wasn't about him, rather it pointed to Messiah.
Another important verification of this occurs in Micah 5. In the same passage where God identifies Bethlehem as the birthplace of Messiah, He adds in verses 3&4, “then the remnant of His brethren shall return to the children of Israel. And He shall stand and feed His flock in the strength of the LORD, in the majesty of the name of the LORD His God.”
So God characterizes Israel as lost sheep, and points to Messiah as the shepherd who will re-gather and feed them. Now watch how Yeshua's proclamations galvanize His role as the prophesied Messiah.
In dealing with the Gentile Canaanite woman in Matthew 15, Jesus boldly spoke in verse 24, “I was not sent except to the lost sheep of the house of Israel.” Earlier in Matthew 10:6, as He sent out His Apostles to minister, He instructed them, “But go rather to the lost sheep of the house of Israel.”
A good amount of John 10 is dedicated to Yeshua as the shepherd, and the villification of the false shepherds, thus dealing with the fulfillment of the prophecies. Making the ultimate connection in verse 11, Jesus said, “I am the good shepherd. The good shepherd gives His life for the sheep.”
However, in the quintessential definition of Messiah, He adds in verse 16, “And other sheep I have which are not of this fold; them also I must bring, and they will hear My voice; and there will be one flock and one shepherd.”
While the lost sheep are clearly Israel, all of mankind needed a Shepherd/Savior. Jesus, by both His words and his actions, completed God’s plan for redemption. As He said, one flock, one shepherd.