7 “Out of my hand,” and “out of my Father's hand.” What is this, “No one plucks them out of my hand,” and “No one plucks them out of my Father's hand”? Have the Father and Son one hand, or is the Son Himself, shall we say, the hand of His Father? If by hand we are to understand power, the power of Father and Son is one; for their Godhead is one. But if we mean hand in the way spoken of by the prophet, “And to whom is the arm of the Lord revealed?” the Father's hand is the Son Himself, which is not to be so understood as if God had the human form, and, as it were, bodily members: but that all things were made by Him.
For men also are in the habit of calling other men their hands, by whom they get done what they wish. And sometimes also the very work done by a man's hand is called his hand; as one is said to recognize his hand when he recognizes what he has written. Since, then, there are many ways of speaking of the hand of a man, who literally has a hand among the members of his body; how much rather must there be more than one way of understanding it, when we read of the hand of God, who has no bodily form?
And in this way it is better here, by the hand of the Father and Son, to understand the power of the Father and the Son; lest, in taking here the hand of the Father as spoken of the Son, some carnal thought also about the Son Himself should set us looking for the Son as somehow to be similarly regarded as the hand of Christ. Therefore, “no one plucks them out of my Father's hand;” that is, no one plucks them from me.
Source: Tractates on the Gospel of John (New Advent)