More deep wisdom from A Course in Miracles clearly describing the lesson that miracles were sent to teach:

"The miracle returns the cause of fear to you who made it.  But it also shows that, having no effects, it is not cause, because the function of causation is to have effects.  And where effects are gone, there is no cause.  Thus is the body healed by miracles because they show the mind made sickness, and employed the body to be the victim, or effect of what it made.  Yet half the lesson will not teach the whole.  The miracle is useless if you learn but that the body can be healed, for this is not the lesson that it was sent to teach. the lesson is the mind was sick that thought the body could be sick; projecting out its guilt caused nothing and had no effects.

"This world is full of miracles.  They stand in shinning silence next to every dream of pain and suffering, of sin and guilt.  They are the dream's alternative, the choice to be the dreamer, rather than deny the active role in making up the dream.  They are the glad effect of taking back the consequence of sickness to its cause.  The body is released because the mind acknowledges 'this is not done to me, but I am doing this'.  And thus the mind if free to make another choice instead.  Beginning here, [healing] will proceed to change the course of every step in the descent to separation, until all the steps have been retraced, the ladder gone, and all the dreaming of the world undone.

"....When you accept a miracle, you do not add your dream of fear to one that is already being dreamed.  Without support the dream will fade away without effects.  For it is your support that strengthens it.

"No mind is sick until another mind agrees that they are separate.  And thus it is their joint decision to be sick.  If you withhold agreement and accept the part you play in making sickness real, the other mind cannot project its guilt without your aid in letting it perceive itself as separate and apart from you.  Thus is the body not perceived as sick by both your minds from separate points of view.  Uniting with [another's] mind prevents the cause of sickness and perceived effects.  Healing is the effect of minds that join, as sickness comes from minds that separate.

"The miracle does nothing just because the minds are joined, and cannot separate.  Yet in the dreaming has this been reversed, and separate minds are seen as bodies, which are separated and which cannot join.  Do not allow...[another] to be sick, for if he is, have you abandoned him to his own dream by sharing it with him.  He has not seen the cause of sickness where it is, and you have overlooked the gap between you, where the sickness has been bred.  Thus are you joined in sickness, to preserve the little gap unhealed, where sickness is kept carefully protected, cherished, and upheld by firm belief, lest [Truth] shall come to bridge the little gap that leads to [It].  Fight not [Its] coming with illusions, for it is [Its] coming that you want above all things that seem to glisten in the dream.

"The end of dreaming is the end of fear, and love was never in the world of dreams. The gap is little.  Yet it holds the seeds of pestilence and every form of ill, because it is a wish to keep apart and not to join.  And thus it seems to give a cause to sickness which is not its cause.  The purpose of the gap is all the cause that sickness has.  For it was made to keep you separated, in a body which you see as if it were the cause of pain.

"The cause of pain is separation, not the body which is only its effect.  Yet separation is but empty space, enclosing nothing, doing nothing, and as unsubstantial as the empty place between the ripples that a ship has made in passing by.   And covered just as fast, as water rushes in to close the gap, and as the waves in joining cover it.  Where is the gap between the waves when they have joined, and covered up the space which seemed to keep them separate for a little while?  Where are the grounds for sickness when the minds have joined to close the little gap between them, where the seeds of sickness seem to grow?

"[Truth] builds the bridge, but only in the space left clean and vacant by the miracle.  The seeds of sickness and the shame of guilt [It] cannot bridge for [it] cannot destroy the alien will that [it] created not.  Let its effects be gone and clutch them not with eager hands to keep them for yourself.  The miracle will brush them all aside, and thus make room for [Truth] Who wills to come and bridge [our] returning to [Itself].

"....What is the world except a little gap perceived to tear eternity apart, and break it into days and months and years?  And what are you who live within the world except a picture of [Life] in broken pieces, each concealed within a separate and uncertain bit of clay?

"Be not afraid, but let your world be lit by miracles.  And where the gap was seen to stand between you, join your [sister] there.  and sickness will be seen without a cause.  The dream of healing in forgiveness lies, and gently shows you that you never sinned.  The miracle would leave no proof of guilt to bring you witness to what never was....

"Accepting [healing] for yourself means not giving support to someone's dream of sickness and of death.  It means that you share not his wish to separate, and let him turn illusions on himself.  Nor do you wish that they be turned, instead, on you.  Thus have they no effects.  And you are free of dreams of pain because you let him be.  Unless you help him, you will suffer pain with him because that is your wish.  And you become a figure in his dream of pain, as he in yours.  So do you both become illusions, and without identity.  You could be anyone or anything, depending on whose evil dream you share.  You can be sure of just one thing; that you are evil, for you share in dreams of fear.

"There is a way of finding certainty right here and now.  Refuse to be a part of fearful dreams whatever form they take, for you will lose identity in them.  You find yourself by not accepting them as causing you, and giving you effects.  You stand apart from them, but not apart from him who dreams them.  Thus you separate the dreamer from the dream, and join in one, but let the other go.  The dream is but illusion in the mind.  And with the mind you would unite, but never with the dream.  It is the dream you fear and not the mind.  You see them as the same because you thing that you are but a dream.  And what is real and what is but illusion in yourself you do not know and cannot tell apart.

"Like you, your brother thinks he is a dream.  Share not in his illusion of himself, for your identity depends on his reality.  Think, rather, of him as a mind in which illusions still persist, but as a mind which brother is to you.  He is not brother made by what he dreams, nor is his body, 'hero' of the dream, your brother.  It is his reality that is your brother, as is yours to him.  Your mind and his are joined in brotherhood.  His body and his dreams but seem to make a little gap, where yours have joined with his.

"And yet, between your minds there is no gap.  To join his dreams is thus to meet him not, because his dreams would separate from you.  Therefore release him, merely by your claim on brotherhood and not on dreams of fear.  Let him acknowledge who he is, by not supporting his illusions by your faith, for if you do, you will have faith in yours.  With faith in yours he will not be released, and you are kept in bondage to his dreams.  And dreams of fear will haunt the little gap, inhabited but by illusions which you have supported in each other's minds.

"Be certain, if you do your part, he will do his, for he will join you where you stand.  Call not to him to meet you in the gap between you, or you must believe that it is your reality as well as his.  You cannot do his part, but this you do when you become a passive figure in his dreams, instead of dreamer of you own.  Identity in dreams is meaningless because the dreamer and the dream are one.  Who shares a dream must be the dream he shares, because by sharing is a cause produced.

"You share confusion and you are confused, for in the gap no stable self exists.  What is the same seems different, because what is the same appears to be unlike.  His dreams are yours because you let them be.  But if you took your own way would he be free of them, and of his own as well.  Your dreams are witness to his, and his attest to the truth of yours.  Yet if you see there is no truth in yours, his dreams will go, and he will understand what made the dream.

"[Wisdom] is in both your minds, and [It] is One because there is no gap that separates [Its] Oneness from Itself.  The gap between your bodies matters not for what is joined in [It] is always one.  No one is sick if someone else accepts his union with him.  His desire to be a sick and separated mind can not remain without a witness or a cause.  And both are gone if someone wills to be united with him.  He has dreams that he was separated from his brother who, by sharing not his dream, has left the space between them vacant.  And [Wisdom] comes to join....

"[Wisdom's] function is to take the broken picture of [ourselves] and put the pieces into place again.  This holy picture, healed entirely does [It] hold out to every separate piece that thinks it is a picture in itself.  To each [It] offers its Identity, which the whole picture represents, instead of just a little, broken bit that he insisted was himself.  And when he sees this picture he will recognize himself.  If you share not your brother's evil dream, this is the picture that the miracle will place within the little gap, left clean of all the seeds of sickness and of sin....

"....The forms the broke pieces seem to take mean nothing.  For the whole is in each one.  And every aspect of [each of us] is just the same as every other part.

"Join not your [sister's] dreams, but join with her, and where you join [her] [Wisdom] is....The seeds of sickness come from the belief that there is joy in separation, and its giving up would be a sacrifice.  But miracles are the result when you do not insist on seeing in the gap what is not there.  Your willingness to let illusions go is all that [Wisdom] requires.  [It] will place the seeds of healing where the seeds of sickness were.  And there will be no loss, but only gain.

"What is a sense of sickness but a sense of limitation?  Of a splitting off and separating from?  A gap perceived between yourselves and what is seen as health?  The good is seen outside; the evil, in.  And thus is sickness separating off the self from good, and keeping evil in.  [Love] is the alternate to dreams of fear.  Who shares in them, can never share in [It].  There is no other choice.  Except you share it, nothing can exist.  And you exist because [Life] shared [Its] Will with you, that [Its] creation might create.

"....Where fear has gone there love must come, because there are but these alternatives.  Where one appears the other disappears.  And which you share becomes the only one you have.  You have the one that you accept, because it is the only one you wish to have.

"....Sickness is anger taken out upon the body, so that it will suffer pain.  It is the obvious effect of what was made in secret, in agreement with another's secret wish to be apart from you as you would be apart from [her].  Unless you both agree that is your wish, it can have no effects.  Whoever says, 'There is no gap between my mind and yours' has kept [Life's] promise, not [her] tiny oath to be forever faithful unto death.  And by [her] healings is [her sister] healed.

"Let this be your agreement with each one; that you be one with [her] and not apart.  And [she] will keep the promise that you make with [her] because it is the one that [she] has made to [Life], as [Life] has made to [her]."