why did he say these things?


"
And the plan which they devised about me to release their Error and their senselessness - I did not succumb to them as they had planned. But I was not afflicted at all. Those who were there punished me. And I did not die in reality but in appearance [...]

For my death, which they think happened, (happened) to them in their error and blindness, since they nailed their man unto their death.[...]

It was another, their father, who drank the gall and the vinegar; it was not I. [...] it was another, Simon, who bore the cross on his shoulder. It was another upon Whom they placed the crown of thorns. But I was rejoicing in the height over all the wealth of the archons and the offspring of their error, of their empty glory. And I was laughing at their ignorance.
[...]
"

- The Second Treatise of the Great Seth


"
The Savior said to me, "He whom you saw on the tree, glad and laughing, this is the living Jesus. But this one into whose hands and feet they drive the nails is his fleshly part, which is the substitute being put to shame, the one who came into being in his likeness. But look at him and me."

But I, when I had looked, said "Lord, no one is looking at you. Let us flee this place."

But he said to me, "I have told you, 'Leave the blind alone!'. And you, see how they do not know what they are saying. For the son of their glory instead of my servant, they have put to shame."
"

- Coptic Apocalypse of Peter


"And they also praise people who preach this falsehood, people who will come after you. They will hold on to the name of a dead man, thinking that in this way they will become pure, but instead they will become more and more defiled. They will fall into a name of error and into the hand of an evil deceiver with complicated doctrines, and they will be dominated by heresy.

[...]”For look, those who will bring judgment on themselves are approaching and will put themselves to shame. They cannot touch me. Peter, you will stand in their midst, but don’t be afraid, though you are fainthearted. Their understanding will be gone, for the invisible one has taken a stand against them.”

When he said this, I saw him apparently being arrested by them. I said, “What do I see, Lord? Is it really you they are seizing, and are you holding on to me? And who is the one smiling and laughing above the cross? Is it someone else whose feet and hands they are hammering?”

The Savior said to me, “The one you see smiling and laughing above the cross is the living Jesus. The one into whose hands and feet they are driving nails is his fleshly part, the substitute for him. They are putting to shame the one who came into being in the likeness of the living Jesus. Look at him and look at me.”[...]
"

- The Revelation of Peter


"
The master appeared to him. He stopped praying, embraced him, and kissed him, saying, “Rabbi, I’ve found you. I heard of the sufferings you endured, and I was greatly troubled. [...] They must be judged for what they have done, for what they have done is not right.”

The master said, “James, do not be concerned for me or these people. I am the one who was within me. Never did I suffer at all, and I was not distressed. These people did not harm me. Rather, all this was inflicted upon a figure of the rulers, and it was fitting that this figure should be [destroyed] by them.
"
- The First Revelation of James



and why did the Quran say this?

“And because of their saying (in boast), ‘We killed Messiah Jesus, son of Mary, the Messenger of God,’ – but they killed him not, nor crucified him, but the resemblance of Jesus was put over another man (and they killed that man), and those who differ therein are full of doubts. They have no (certain) knowledge, they follow nothing but conjecture. For surely; they killed him not.

Surah 4:157