I have been reading, and greatly benefiting from, the chapters on the resurrection in Thomas F. Torrance, Atonement: The Person and Work of Christ, which is drawn from his lectures which formed the basis of his Space, Time and Resurrection. So far Torrance has been the most helpful theologian I have read on the resurrection after Richard Gaffin and N.T. Wright. From p. 221 (italics his):
“What Jesus Christ is in his resurrection, he is in himself. The resurrection was not just an event that happened to Christ, for it corresponded to the kind of person he was in his own being.”
My paraphrase: it was impossible for Jesus to remain dead, because being resurrected was part of who he was. Resurrection was exponential of his identity. His very life was such that death could not overtake it, but must be overtaken and swallowed up by it. “I am resurrection and the life” (John 11:25). “I am … the life” (John 14:26). Just as the resurrection is an a posteriori argument for Christ’s deity, his deity is an a priori argument for his resurrection. Why was Jesus Christ raised? Because it was who he was – eternal, life-spilling-over God – to be so.
Here is a later passage from Torrance which reveals his meaning more fully (236):
“The actual resurrection of Jesus from the tomb was recognized to be in entire accordance with his nature and person – but that was the stupendous thing about it. This was not just a miracle, not some wonderful event or portent, but something which in all its wonderfulness was not a whit different from the essential nature of the risen one in himself. And what is more, it corresponded to the claim of Jesus, as given in the Johannine literature, ‘I am the resurrection and the life.’ ‘I am the truth.’ He is himself the reality of the resurrection and the new life that breaks through and out of death. He is the creator-God among mankind, at work even in the midst of death and corruption and perdition and nothingness.
With this recognition of the utter consistency between the resurrection event and the essence of the resurrected one, came the full realisation that the whole life of Jesus, together with his resurrection, was the manifestation among men and women and on earth and in time of the ultimate and original and final creative activity of God. That is why the resurrection is so baffling to thought and observation.”