Commenting on John 10:30, J. H. Bernard, D.D. says in A Critical and Exegetical Commentary on the Gospel According to St. John:
“A unity of fellowship, of will, and of purpose between the Father and the Son is a frequent theme in the Fourth Gospel..., and it is tersely and powerfully expressed here; but to press the words so as to make them indicate identity of ousia [Greek for ‘substance,’ ‘essence’], is to introduce thoughts that were not present to the theologians of the first century."[1]
Even the very trinitarian New Testament Greek scholar W. E. Vine when discussing the Greek word for “one” says: “(b) metaphorically [figuratively], union and concord, e.g., John 10:30; 11:52; 17:11, 21, 22....” - An Expository Dictionary of New Testament Words, p. 809.
Trinitarian Professor William Barclay writing in his popular Daily Study Bible Series, The Gospel of John, Vol. 2, The Westminster Press, 1975, pp. 74, 75, 76 says:
“Now we come to the supreme claim [of John 10:30]. ‘I and the Father are one,’ said Jesus. What did he mean? Is it absolute mystery, or can we understand at least a little of it? Are we driven to interpret it in terms of essence and hypostasis and all the rest of the metaphysical and philosophic notions about which the makers of creeds fought and argued? Has one to be a theologian and a philosopher to grasp even a fragment of the meaning of this tremendous statement?
“If we go to the Bible itself for the interpretation,” continues Barclay, “we find that it is in fact so simple that the simplest mind can grasp it. Let us turn to the seventeenth chapter of John’s Gospel, which tells of the prayer of Jesus for his followers before he went to his death: ‘Holy Father, keep them in thy name, which thou hast given me, that they may be one, even as we are one’ (John 17:11). Jesus conceived of the unity of Christian with Christian as the same as his unity with God.”
“Here is the essence of the matter”, says Barclay. “The bond of unity is love; the proof of love is obedience. Christians are one with each other when they are bound by love, and obey the words of Christ. Jesus is one with God, because as no other ever did, he obeyed and loved him. His unity with God is a unity of perfect love, issuing in perfect obedience.[2]
"When Jesus said: ‘I and the father are one,’ he was not moving in the world of philosophy and metaphysics and abstractions; he was moving in the world of personal relationships. No one can really understand what a phrase like ‘a unity of essence’ means; but any one can understand what a unity of heart means. Jesus’s unity with God came from the twin facts of perfect love and perfect obedience. He was one with God because he loved and obeyed him perfectly....”