Who are the sheep? The ones who listen and follow. Jesus doesn't save those who decided to reject him. The sheep and goats are metaphors for people who believe in Christ and people who don't.
Jesus does tell us who He dies for, so what you and many others are doing is adding on to His words.
John 10:11
“I am the good shepherd. The good shepherd gives His life for the sheep.
John 10:15
As the Father knows Me, even so I know the Father; and I lay down My life for the sheep.
Christ also mentions about 'other sheep I have'. God knows those who will be His who are not yet His, That is due to God's foreknowing of them as His people, so they are the other sheep.
So Christ only dies for the sheep who belong or will belong to Christ. The non sheep belong not to God as they will never be of God, they are the children of the devil.
1 John 3:9-10
New King James Version
9 Whoever has been born of God does not sin, for His seed remains in him; and he cannot sin, because he has been born of God.
10 In this the children of God and
the children of the devil are manifest: Whoever does not practice righteousness is not of God, nor is he who does not love his brother.
Notice Christ says He must go and get these other sheep he has.
They WILL hear, the result is there WILL be one flock, and one shepherd.
Obviously these other sheep have not yet heard, And they are not the children of the devil, they are different even though they do not yet believe in Christ, they will believe. But they are like the children of the devil, just like Ephesians 2 says of the 'others' who in that chapter ore evil children of the devil. Others tells us about a different group from the main core.
John 10:15-17
New King James Version
15 As the Father knows Me, even so I know the Father; and I lay down My life for the sheep.
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.
17 “Therefore My Father loves Me, because I lay down My life that I may take it again.
Ephesians 2
And you He made alive, who were dead in trespasses and sins, 2 in which you once walked according to the course of this world, according to the prince of the power of the air, the spirit who now works in the sons of disobedience, 3 among whom also we all once conducted ourselves in the lusts of our flesh, fulfilling the desires of the flesh and of the mind,
and were by nature children of wrath, just as the others.
So even though they were not children of the devil, they were still by their nature children of wrath, not yet being born of God.
But of course God foreknew them as His people so God makes them alive according to His love for His foreknown to Him people. God does not make everyone alive, He only makes alive those He foreknows as His whom He loves. This is a God thing, not a human thing. God is the author of you faith, your faith was given, granted to you and had nothing at all to do with your thoughts or actions.
4 But God, who is rich in mercy, because of His great love with which He loved us, 5 even when we were dead in trespasses, made us alive together with Christ (by grace you have been saved), 6 and raised us up together, and made us sit together in the heavenly places in Christ Jesus, 7 that in the ages to come He might show the exceeding riches of His grace in His kindness toward us in Christ Jesus.
You have been saved by His grace because of His love for you by the means of faith which He also granted to you.
8 For by grace you have been saved through faith, and that not of yourselves; it is the gift of God,