Holding grievances is an attack on God's plan for salvation.

While we have recognized that the ego's plan for salvation is the opposite of God's, we have not yet emphasized that it is an active attack on His plan, and a deliberate attempt to destroy it. In the attack, God is assigned the attributes which are actually associated with the ego, while the ego appears to take on the attributes of God.
The ego's fundamental wish is to replace God. In fact, the ego is the physical embodiment of that wish. For it is that wish that seems to surround the mind with a body, keeping it separate and alone, and unable to reach other minds except through the body that was made to imprison it. The limit on communication cannot be the best means to expand communication. Yet the ego would have you believe that it is.
Although the attempt to keep the limitations that a body would impose is obvious here, it is perhaps not so apparent why holding grievances is an attack on God's plan for salvation. But let us consider the kinds of things you are apt to hold grievances for. Are they not always associated with something a body does? A person says something you do not like. He does something that displeases you. He "betrays" his hostile thoughts in his behavior.
You are not dealing here with what the person is. On the contrary, you are exclusively concerned with what he does in a body. You are doing more than failing to help in freeing him from the body's limitations. You are actively trying to hold him to it by confusing it with him, and judging them as one. Herein is God attacked, for if His Son is only a body, so must He be as well. A creator wholly unlike his creation is inconceivable.
If God is a body, what must His plan for salvation be? What could it be but death? In trying to present Himself as the Author of life and not of death, He is a liar and a deceiver, full of false promises and offering illusions in place of truth. The body's apparent reality makes this view of God quite convincing. In fact, if the body were real, it would be difficult indeed to escape this conclusion. And every grievance that you hold insists that the body is real. It overlooks entirely what your brother is. It reinforces your belief that he is a body, and condemns him for it. And it asserts that his salvation must be death, projecting this attack onto God, and holding Him responsible for it.
To this carefully prepared arena, where angry animals seek for prey and mercy cannot enter, the ego comes to save you. God made you a body. Very well. Let us accept this and be glad. As a body, do not let yourself be deprived of what the body offers. Take the little you can get. God gave you nothing. The body is your only savior. It is the death of God and your salvation.
This is the universal belief of the world you see. Some hate the body, and try to hurt and humiliate it. Others love the body, and try to glorify and exalt it. But while the body stands at the center of your concept of yourself, you are attacking God's plan for salvation, and holding your grievances against Him and His creation, that you may not hear the Voice of truth and welcome It as Friend. Your chosen savior takes His place instead. It is your friend; He is your enemy.
We will try today to stop these senseless attacks on salvation. We will try to welcome it instead. Your upside-down perception has been ruinous to your peace of mind. You have seen yourself in a body and the truth outside you, locked away from your awareness by the body's limitations. Now we are going to try to see this differently.
The light of truth is in us, where it was placed by God. It is the body that is outside us, and is not our concern. To be without a body is to be in our natural state. To recognize the light of truth in us is to recognize ourselves as we are. To see our Self as separate from the body is to end the attack on God's plan for salvation, and to accept it instead. And wherever His plan is accepted, it is accomplished already.
Our goal in the longer practice periods today is to become aware that God's plan for salvation has already been accomplished in us. To achieve this goal, we must replace attack with acceptance. As long as we attack it, we cannot understand what God's plan for us is. We are therefore attacking what we do not recognize. Now we are going to try to lay judgment aside, and ask what God's plan for us is:

What is salvation, Father? I do not know.
Tell me, that I may understand.

Then we will wait in quiet for His answer. We have attacked God's plan for salvation without waiting to hear what it is. We have shouted our grievances so loudly that we have not listened to His Voice. We have used our grievances to close our eyes and stop our ears.
Now we would see and hear and learn. "What is salvation, Father?" Ask and you will be answered. Seek and you will find. We are no longer asking the ego what salvation is and where to find it. We are asking it of truth. Be certain, then, that the answer will be true because of Whom you ask.
Whenever you feel your confidence wane and your hope of success flicker and go out, repeat your question and your request, remembering that you are asking of the infinite Creator of infinity, Who created you like Himself:

What is salvation, Father? I do not know.
Tell me, that I may understand.

He will answer. Be determined to hear.
One or perhaps two shorter practice periods an hour will be enough for today, since they will be somewhat longer than usual. These exercises should begin with this:

Holding grievances is an attack on God's plan
for salvation. Let me accept it instead.
What is salvation, Father?

Then wait a minute or so in silence, preferably with your eyes closed, and listen for His answer.

- Jesus Christ in A Course in Miracles, Lesson 72