John 10:27-30
“For My sheep hear My voice, and follow Me; and I give unto them eternal life; neither can any man pluck them out of My hand. The Father, which gave them Me, is greater than all, and no man is able to pluck them out of My Father's hand. I and the Father are One.”
Observe how in renouncing He excites them to follow Him. “You hear Me not,” He says, “for neither are you sheep, but they who follow, these are of the flock.” This He said, that they might strive to become sheep. Then by mentioning what they should obtain, He makes these men jealous, so as to rouse them, and cause them to desire such things.
“What then? Is it through the power of the Father that no man plucks them away, and have you no strength, but art too weak to guard them?” By no means. And in order that you may learn that the expression, “The Father which gave them to Me,” is used on their account, that they might not again call Him an enemy of God, therefore, after asserting that, “No man plucks them out of My hand,” He proceeds to show, that His hand and the Father's is One. Since had not this been so, it would have been natural for Him to say, “The Father which gave them to Me is greater than all, and no man can pluck them out of My hand.” But He said not so, but, “out of My Father's hand.” Then that you may not suppose that He indeed is weak, but that the sheep are in safety through the power of the Father, He adds, “I and the Father are One.” As though He had said “I did not assert that on account of the Father no man plucks them away, as though I were too weak to keep the sheep. For I and the Father are One.” Speaking here with reference to Power, for concerning this was all His discourse; and if the power be the same, it is clear that the Essence is also. And when the Jews used ten thousand means, plotting and casting men out of their synagogues, He tells them that all their contrivances are useless and vain; “For the sheep are in My Father's hand”; as the Prophet says, “Upon My hand I have pictured your walls.” Then to show that the hand is One, He sometimes says that it is His own, sometimes the Father's. But when you hear the word “hand,” do not understand anything material, but the power, the authority. Again, if it was on this account that no one could pluck away the sheep, because the Father gave Him power, it would have been superfluous to say what follows, “I and the Father are One.” Since were He inferior to Him, this would have been a very daring saying, for it declares nothing else than an equality of power; of which the Jews were conscious, and took up stones to cast at Him. Yet not even so did He remove this opinion and suspicion; though if their suspicion were erroneous, He ought to have set them right, and to have said, “Wherefore do ye these things? I spoke not thus to testify that my power and the Father's are equal”; but now He does quite the contrary, and confirms their suspicion, and clenches it, and that too when they were exasperated. For He makes no excuse for what had been said, as though it had been said ill, but rebukes them for not entertaining a right opinion concerning Him. For when they said,
Source: Homilies on the Gospel of John (New Advent)