John 1:29
The next day John seeth Jesus coming unto him, and saith, Behold the Lamb of God, which taketh away the sin of the world.
This is also the World John writes of in his Epistle when writing of the propitiation of Christ taking away our Sins 1 Jn 2:2
2 And he is the propitiation for our sins: and not for ours only, but also for the sins of the whole world.
1 Jn 3:5
And ye know that he was manifested to take away our sins; and in him is no sin.
1 Jn 4:10
Herein is love, not that we loved God, but that he loved us, and sent his Son to be the propitiation for our sins.
Now being the propitiation for our sins, and taking them away are one and the same. His Death was that satisfaction to Gods Law and Justice to take away our sins, and that could not be the case if were not absolved of, acquitted from, justified from them all before God. Doesn't the resurrection of Christ testify the same Rom 4:25
Who [The Lamb of God] was delivered for our offences, and was raised again for[because of] our justification.
So that World in Jn 1:29 is a Justified world with no sin charged to it 2 Cor 5:19 because they've been taken away, so it cant apply to all without exception ! Some will yet die in their sins Jn 8:21,24
The main issue I immediately notice is: you seem to be equating the fact that Jesus is the sacrificial lamb for all sins and the propitiation (atoning sacrifice which brings us into relationship with God), with completion of the entire atonement process. Being the sacrifice for every sin is not the same thing as saying the atonement process was completed for all sinners, the sinner has a part to play.
God would have no problem forgiving, God is totally fair and just, but any rebellious disobedient child needs more than just forgiveness, since, if at all possible, a wonderful parent would see to the fair/just Loving discipline of His children for all the benefits discipline provides. Atonement thus is a disciplining process we go through with God and Christ as we are crucified “with Christ”.
The Jews under the Law would have a good understanding of atonement by experiencing atonement for very minor sins which took little disciplining:
Lev.4 starts atonement off giving details of what the priest must do, which you should read and understand, but Lev.5 gets into more detail about the individual, so please read Lev. 5 with much thought. I find people with pet theories of atonement skip Lev. 5 all together and might go to Lev. 16, but the day of atonement has some lite symbolic references to Christ in Lev. 16 while, Lev 5 is a closer representation. I will discuss Lev. 16 if you want to take the time, but it takes some explaining of what and why it was needed by itself. Please read Lev. 5 before going further.
Atonement is much more than the sacrifice itself; it is a process which we can see from the Old Testament examples of the atonement process.
We can start with Lev. 5: 3 or if they touch human uncleanness (anything that would make them unclean) even though they are unaware of it, but then they learn of it and realize their guilt; 4 or if anyone thoughtlessly takes an oath to do anything, whether good or evil (in any matter one might carelessly swear about) even though they are unaware of it, but then they learn of it and realize their guilt— 5 when anyone becomes aware that they are guilty in any of these matters, they must confess in what way they have sinned. 6 As a penalty for the sin they have committed, they must bring to the Lord a female lamb or goat from the flock as a sin offering; and the priest shall make atonement for them for their sin. … 10 The priest shall then offer the other as a burnt offering in the prescribed way and make atonement for them for the sin they have committed, and they will be forgiven.
Lev. 5 is talking about some really minor sins almost accidental sins and very much unintentional sins, there is no atonement process at this time for major sins, intentional direct disobedience toward God (these require banishment or death of the sinner).
The atonement process includes confessing, securing a good offering, personally bringing the offering to the priests at the temple altar, the priest has to offer it correctly and after the atonement process is correctly completed the sinner’s sins will be forgiven.
Note also the relationship between the sinner and the offering, the offering is “as a penalty for the sin” and not a replacement for the sinner. The idea of “penalty” is a “punishment” for the sinner, yet punishment of your child is better translated “disciplining”.
Reading all of Lev. 5: we have a lamb, two doves and a bag of flour all being an atoning sacrifice for the exact same sin, but vary with the wealth of the sinner, yet God does not consider the wealthy person of great value then the poor person, so what is happening? We can only conclude there is an attempt to equalize the hardship on the sinner (penalty/punishment/discipline). In fact, this might be the main factor in the atonement process at least in Lev. 5. God is not only forgiving the sins, but seeing to the discipling of the sinner (like any Loving parent tries to do if possible). The problem is, it can only be done for minor sins at this time.
Please notice there is an “and” just before “they will be forgiven”, suggesting a separate action, so the forgiveness is not part of the atonement process, but comes afterwards (this will be discussed more later).
Do you see the benefit for the Jewish people (nothing really to help God out here) going through this atonement process? That rich person had to water, feed, hang on to a lamb, he is not the lamb’s shepherd, so for hours waiting in line to get to the priest he fighting this lamb and the poor person may have skipped meals to get that bag of flour, so he has an equal hardship also. They are going to be more careful in the future and those around them will not want to go through the same thing. Yes, they can experience worship, forgiveness, and fellowship in the process.
We should be able to extrapolate up from extremely minor sins to rebellious disobedience directly against God, but that is a huge leap, so the hardship on the sinner will have to be horrendous, the sacrifice of much greater value (penalty for the sinner), and this will take a much greater Priest.