Perhaps you underestimating Jesus’ Sacrifice. Jesus’ Sacrifice is just as applicable to past sins as it is to future sins. In other words Jesus sacrifice was a one time sacrifice for sin of all times.
I apologize for the length of my answer, but every point seemed necessary to convey the message.
If Jesus sacrifice can extend into the future and atone for our sins today why should it not extend into the past to atone for their sins?
The true key to understanding Jesus sacrifice is in the application of faith. Sins are forgiven through Jesus Christ in reward for faith in the ability of God to forgive our sins. Since the Cross that has been enumerated as faith in Jesus as the only propitiation for sin, but prior to the cross it was based on the belief that God could forgive sin through belief that a blood sacrifice was necessary for the forgiveness of sin, thus the sacrifices of unblemished animals was substitution for the future sacrifice of Jesus.
In all cases whether prior to the cross; or post cross having faith that our sins will be forgiven in return for our trust in the sacrifice of Jesus.
Let's trace sin and its punishment in part of the Bible and see if we can determine how it is attributed, to both us, and our sins to Jesus; and how it is forgiven.
Since almost everyone is familiar with the story of the fall of mankind; I will only point out a couple of things about it.
God had told Adam that when he ate of the tree he would surely die; and yet they succumbed to the lie of Satan that they would not die.
All scripture is quoted from the New King James translation, unless otherwise noted.
Genesis 3:4 Then the serpent said to the woman, "You will not surely die.
and sadly all generations after them have fallen for the same lie. That then is the first breech of faith.
Genesis 6:5 through 7 Then the LORD saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually.
6 And the LORD was sorry that He had made man on the earth, and He was grieved in His heart. 7 So the LORD said, "I will destroy man whom I have created from the face of the earth, both man and beast, creeping thing and birds of the air, for I am sorry that I have made them."
Sin is so abhorrent to God, that he decided to obliterate his whole creation and the thing that saved mankind was the faith of one man Noah. And even though he has promised not to destroy the world again with water he has not promised not to do so with fire.
Genesis 8:21 and 22 And the LORD smelled a soothing aroma. Then the LORD said in His heart, "I will never again curse the ground for man's sake, although the imagination of man's heart is evil from his youth; nor will I again destroy every living thing as I have done. 22 "While the earth remains, Seedtime and harvest, Cold and heat, Winter and summer, And day and night Shall not cease."
Genesis 13:13 But the men of Sodom were exceedingly wicked and sinful against the LORD.
Genesis 19:24 and 25 Then the LORD rained brimstone and fire on Sodom and Gomorrah, from the LORD out of the heavens. 25 So He overthrew those cities, all the plain, all the inhabitants of the cities, and what grew on the ground.
And in this same story he:
Genesis 19:17 So it came to pass, when they had brought them outside, that he said, "Escape for your life! Do not look behind you nor stay anywhere in the plain. Escape to the mountains, lest you be destroyed."
Genesis 19:26 But his wife looked back behind him, and she became a pillar of salt.
At this point we have established three things:
God so hates sin that he is willing to destroy his creations in order to eradicate it.
God does and will hold each of us accountable for our sins.
God will punish sin with death and he is willing to use fire to cleanse sin from his creation which includes mankind.
Knowing this it is not that hard to accept:
Revelation 20:14 Then Death and Hades were cast into the lake of fire. This is the second death.
Revelation 21:8 But the cowardly, unbelieving, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars shall have their part in the lake which burns with fire and brimstone, which is the second death."
Thankfully though that is not the end of the Story.
John 3:16 and 17 For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. 17 For God did not send His Son into the world to condemn the world, but that the world through Him might be saved.
The question now becomes why he loves us so much and exactly how does Jesus death on the cross and his resurrection atone for our sins.
To answer these questions it is necessary to understand what death really refers to and just how they are attributed to Jesus.
So let's start with death and see if we can determine what God considers death to be.
We have already determined that there are two deaths, since if there is a second death there must therefore be a first death.
The first death is a physical death which has to do with the physical body only.
Genesis 2:7 And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living being.
Genesis 2:7 KJV And the LORD God formed man of the dust of the ground, and breathed into his nostrils the breath of life; and man became a living soul.
Although the King James translation and the New King James version differ in that the NKJV says being and the KJV says Soul, they are both correct in that man became both
The difference here is that being refers to man's perishable body and soul refers to his in non-perishable eternal personage.
The physical body suffers the first death and the non-perishable Soul suffers the second death.
God in his omniscience knew before he created the Universe, that man would not be able to not sin; but God had a reason for creating the Universe of which we remain ignorant to this day. But apparently God had a specific reason for creating man in their image.
So if man was ever to be able to fulfill those exaptation's he therefore had to improvise some form of redemption for man. According to the words of Jesus in John 3:16 the reason was his great love for us.
God could have just as easily created man without free will, but if we have learned anything about love it is that it must be freely given; and that goes both ways; not only our love for God but his love for us. That is the reason Salvation is God's grace and cannot be earned. As an example how many people have tried in vain to cause someone to love them.
So now we get down to the hardest part of what Jesus said in John 3:16 for man to accept.
That being that God loved us enough that he gave his only son (Jesus) that our sins be forgiven, based on faith. We must realize two things if we are to ever understand God's great love for us.
- We are incapable of ever comprehending God's ways:
Isaiah 55:8 and 9 For my thoughts are not your thoughts, neither are your ways my ways, saith the LORD. 9 For as the heavens are higher than the earth, so are my ways higher than your ways, and my thoughts than your thoughts.
- God as creator of the Universe retains all power. And therefore has the power to do with any portion of his creation as he sees fit; and he sees fit to forgive our sins, even though he maintains the punishment that he proclaimed in Genesis, that being death is the reward for sin.
So how does Jesus death on the cross pay our sin debt?
If Jesus was to be our propitiation for sin it meant that he must die sinless himself, otherwise his death would be punishment for his sins.
There has to be a way of transferring our sins to Jesus in order that they be atoned for, and that is where Faith enters the picture.
Matthew 9:2 And, behold, they brought to him a man sick of the palsy, lying on a bed: and Jesus seeing their faith said unto the sick of the palsy; Son, be of good cheer; thy sins be forgiven thee.
Matthew 9:22 But Jesus turned him about, and when he saw her, he said, Daughter, be of good comfort; thy faith hath made thee whole. And the woman was made whole from that hour.
Matthew 9:29 Then He touched their eyes, saying, "According to your faith let it be to you."
Notice that in each of these cases it is faith which allowed them to be healed. but in verse 9:2 Jesus said that his sins were forgiven, which is different than healing although he was healed at the same time.
So we see that the key to forgiveness of sin lies in faith, but faith in what way? So let's take a little bit longer look at Matthew chapter 9 verses 27 through 29
Matthew 9:27 through 29 And when Jesus departed thence, two blind men followed him, crying, and saying, Thou Son of David, have mercy on us. 28 And when he was come into the house, the blind men came to him: and Jesus saith unto them, Believe ye that I am able to do this? They said unto him, Yea, Lord. 29 Then touched he their eyes, saying, According to your faith be it unto you.
So here we see that healing which seems to be much the same as forgiving sins is tied to our faith that Jesus is able to do exactly as he says he can do, which can also be extended to be understood as Salvation is directly tied to our faith that Jesus death on the cross paid our sin debt in full, and that his resurrection from the dead is proof of his power over the second death which is the death of the Soul, or eternal punishment in the lake of fire.
hope this helps.