Why does a trinitarian say John 10:30 doesn't teach that Jesus is the essence of God?

[TeeM]

John Calvin: commentary of John 10:30.

" I and my Father are one. He intended to meet the jeers of the wicked; for they might allege that the power of God did not at all belong to him, so that he could promise to his disciples that it would assuredly protect them. He therefore testifies that his affairs are so closely united to those of the Father, that the Father’s assistance will never be withheld from himself and his sheep The ancients made a wrong use of this passage to prove that Christ is (?????????) of the same essence with the Father. For Christ does not argue about the unity of substance, but about the agreement which he has with the Father, so that whatever is done by Christ will be confirmed by the power of his Father."