The key to understand is the sheep must repent, just exactly like he did when first saved as an unbeliever.
That's the point.
Please examine carefully what Jesus says here, and what it takes for a wayward brother to return to Him.
- If a man has a hundred sheep, and one of them goes astray, does he not leave the ninety-nine and go to the mountains to seek the one that is straying?
- And if he should find it, assuredly, I say to you, he rejoices more over that sheep than over the ninety-nine that did not go astray.
Please notice the steps to bringing him back to being "found".
“
Moreover if your brother sins against you,
go and tell him his fault between you and him alone.
- If he hears you, you have gained your brother.
- But if he will not hear, take with you one or two more
- And if he refuses to hear them, tell it to the church.
- But if he refuses even to hear the church, let him be to you like a heathen and a tax collector.
12 “What do you think? If a man has a hundred sheep, and one of them goes astray, does he not leave the ninety-nine and go to the mountains to seek the one that is straying? 13 And if he should find it, assuredly, I say to you, he rejoices more over that sheep than over the ninety-nine that did not go astray. 14 Even so it is not the will of your Father who is in heaven that one of these little ones should perish. 15 “
Moreover if your brother sins against you, go and tell him his fault between you and him alone. If he hears you, you have gained your brother. 16 But if he will not hear, take with you one or two more, that ‘by the mouth of two or three witnesses every word may be established.’ 17 And if he refuses to hear them, tell it to the church. But if he refuses even to hear the church, let him be to you like a heathen and a tax collector. Matthew 18:12-17
JPT