In ACIM, Jesus spells out that forgiveness and atonement are the same thing, and so is true perception. These are all a state in which there is recognition, accurate perception, and a forgiving attitude which sees that there is no sin. Or moreso, it is the acknowledgment and re-acceptance of God's truth and the willingness to accept your permanent innocence, as you are in the Kingdom.
"For true perception is a remedy with many names. Forgiveness, salvation, Atonement, true perception, all are one. They are the one beginning, with the end to lead to oneness far beyond themselves. True perception is the means by which the world is saved from sin, for sin does not exist. And it is this that true perception sees."
You can see that Jesus mingles these terms interchangeably. For example, here Jesus mixes forgiveness with true perception as a way of looking:
"Forgiveness looks on sinlessness alone, and judges not."
"But forgiveness looks past bodies. This is its holiness; this is how it heals."
"This is the shift that true perception brings: What was projected out is seen within, and there forgiveness lets it disappear."
And here he mixes true perception and atonement, also indicating that a forgiving attitude produces atonement, which means it also produces true perception:
"It is concerned only with Atonement, or the correction of perception. The means of the Atonement is forgiveness."
And here he tells us that complete forgiveness, aka true perception, is a state in which you have let guilt go, and have accepted atonement.
"If what you offer IS complete forgiveness, you MUST have LET GUILT GO, accepting the Atonement for yourself, and learning you ARE guiltless."
And here he refers to atonement as the undoing of errors, which is accomplished by forgiveness, which is ITSELF the state of atonement and true perception.
"The sole responsibility of God's teacher is to accept the Atonement for himself. Atonement means correction, or the undoing of errors."
Also how about this:
"Healing and Atonement are not related; they are identical."
"there are no degrees of Atonement. It is the one complete concept possible in this world, because it is the source of a wholly unified perception."
"Accept Atonement and you are healed. Atonement is the Word of God."
"The offer of Atonement is universal. It is equally applicable to all individuals in all circumstances. And in it is the power to heal all individuals of all forms of sickness."
Here is something to consider which might be controversial. Jesus refers to forgiveness as a means of accomplishing atonement, but also as completely synonymous with the atonement itself. Because complete forgiveness is the atonement is the state you enter with true perception. Which means, by implication, that any state prior to acceptance of atonement is NOT forgiveness.
There is a very widely prevalent myth therefore in the ACIM community that we are to "do forgiveness" in order to reach atonement. But atonement IS forgiveness. So what are we to call that which leads UP TO it? Perhaps a better term which Jesus uses is "purification"
"Miracles are everyone's right (miracle mindedness is also the same thing as atonement and true perception), but purification is necessary first."
Now, we need to look at something a bit deeper. The main pivotal cornerstone of the ego's thought system is SIN. Sin can go one of two ways. If you take sin to be real, forgiveness is not justified, and so you become UNforgiving. Sin becomes a condemnation and attack, and you move into guilt.
But when you go the other way, if you take sin and recognize its unreality, untruth, and non-existence, THAT will put you into the state of forgiveness. And in effect, that means this recognition of "there is no sin" IS the atonement, and IS the basis for true perception or corrected perception. It is a forgiving way of seeing (Christ Vision).
This all "hinges" around sin. Don't forgive it and you move into guilt. Forgive it and you move into the recognition of innocence which is true forgiveness.
"From sin comes guilt as surely as forgiveness takes all guilt away."
But let's take it even further.
There are two thought systems. One is the thought system of God which is Heaven and the Kingdom. Reality is run by this thought system because this is where God actually DOES His thinking, and all creative thought OCCURS there. Thats where the thought system IS.
Then, in contrast, the ego thought system, which opposes God's thought system, can be said to be LOCATED on this side of the idea of separation and sin. On this side, where sin is real, the entire contents of being on this side of the fence is unforgiving.
So what Jesus is asking us to do, really, is to take our mind out of the ENTIRE realm of unforgiveness, ie the entire ego thought system, and put it BACK into the Kingdom. Which means crossing over from the thought system of ego to the thought system of God.
What this means is that the Atonement and the acceptance of it, is an acceptance that God's system of thought is true and real, and it's a way of really regaining access to the Mind of God, to the Kingdom, and to your innocent holy self which resides on the OTHER side of the separation divide. Essentially, in another world.
So when we get into the state of forgiveness, in which there is nothing to forgive because sin is recognized as not existing, and thus no sin is perceived as true, it really means we're re-accessing heaven.
To accept atonement is the ONLY cure and the ONLY way to TRULY undo something. "Only atonement can be said to cure", meaning that only in the moment that you accept the truth about you that is IN HEAVEN, does your mind completely change and is cured and healed of its false beliefs.
Accepting atonement on any particular issue should entail you flipping over from the ego thought system to God's thought system. Going from sin and guilt, to innocence. Going from not accepting God's love, to accepting it.
There are actually some statements Jesus makes where he is saying that you do not REALLY change your mind, UNTIL you switch to the holy thought system. Which means getting out of the ego system ENTIRELY and putting your mind back into reality.
"To "change your mind" means to place it at the disposal of True authority. The miracle is thus a sign that the mind has elected to be guided by Christ in HIS service. The abundance of Christ is the natural result of choosing to follow him."
"the power of your simple change of mind: I loose the world from all I thought it was, And choose my own reality instead."
"The tiny change of mind by which the crucifixion is changed to Resurrection. And, being true, it is so simple that it cannot fail to be completely understood."
"Your hand becomes the giver of Christ's touch; your change of mind becomes the proof that who accepts God's gifts can never suffer anything."
"And it will change entirely as you elect to change your mind, and choose the joy of God as what you really want."
Only choosing between TRUTH and ILLUSIONS, is your only choice, which is a choice BETWEEN thought systems, and therefore BETWEEN WORLDS. Either you will accept yourself as you are innocent in Heaven, or will accept yourself as sinful within the ego realm.
"Knowledge cannot dawn on a mind full of illusions, because truth and illusions are irreconcilable. Truth is whole, and CANNOT be known by PART of a mind."
While atonement and thus forgiveness and true perception might well be "illusions" within this world, outside the Kingdom, they are reflections of the Kingdom, and thus reflections of the truth about you IN the Kingdom. Accepting atonement is accepting that you are still as God created you, as you are in the Kingdom.
But Jesus clearly tells us that the FULL acceptance of Atonement SHOULD take you INTO HEAVEN. Whereby even true perception ends.
"Since perception rests on lack, those who perceive have not totally accepted the Atonement and given over themselves to truth. Perception IS a separated state, and the perceiver DOES need healing. Communion, not prayer, is the natural state of those who know. God and HIS miracles (you) are inseparable."
So when thinking of forgiveness, and doing forgiveness, or applying the course, we need to realize that if we DON'T get all the way to the atonement principle on some issue, we HAVE NOT really fully forgiven it. If we still believe that something happened or that sin was real, we are not IN a forgiving state of mind. In order to DO a forgiveness, successfully, essentially REQUIRES that you accept atonement - to accept the truth of your total ongoing innocence, and the complete recognition that there HAS NOT BEEN anything that needs forgiving.
While it seems there is something to forgive, and we think we're doing forgiveness, we actually are NOT doing forgiveness. What we're doing is preparing to enter a state of forgiveness. And that is purification work. But if we do that work, and we don't take it all the way to "nothing happened", "everyone is still innocent as God created us to be", "there is no sin", "sin is not real" etc... then we haven't really gone FAR enough in our change of mind, and are still really WITHIN the ego though system.
That means we've fallen short and the forgiveness is not complete, because we have not moved OVER to hooking our mind up with God, in service to Christ. Remember that mind in the service of Spirit/soul is its natural state, while when mind "goes rogue" and becomes its own tyrannical ruler, it is now in a separated state. To return to forgiveness and accept atonement is to actually put your mind back under the Authority of the Soul, which requires ACCEPTING THE INNOCENT SOUL AS YOUR TRUE SELF.
Only atonement can be said to cure, so we must be willing to go ALL THE WAY to the atonement truth and the acceptance of it, which opens you up to allow yourself to be loved by God, and to RECEIVE A MIRACLE, which you can then extend to others. Short of this, forgiveness is incomplete and atonement is still being avoided. And therefore it is not a complete cure. To truly forgive is to CURE, completely and totally and forever. Acceptance of your permanent innocence and worthiness is the only acceptable goal.