11 But although the wickedness of man can pervert his intellectual powers, nevertheless the words retain their meaning. Our Lord prays to His Father that those who shall believe in Him may be one, and as He is in the Father and the Father in Him, so all may be one in Them. Why do you bring in here an identity of mind, why a unity of soul and heart through agreement of will? For there would have been no lack of suitable words for our Lord, if it were will that made them one, to have prayed in this fashion—Father, as We are one in will, so may they also be one in will, that we may all be one through agreement.
Or could it be that He Who is the Word was unacquainted with the meaning of words? And that He Who is Truth knew not how to speak the truth? And He Who is Wisdom went astray in foolish talk? And He Who is Power was compassed about with such weakness that He could not speak what He wished to be understood? He has clearly spoken the true and sincere mysteries of the faith of the Gospel. And He has not only spoken that we may comprehend, He has also taught that we may believe, saying, That they all may be one, as Thou Father art in Me, and I in You, that they also may be in Us.
For those first of all is the prayer of whom it is said, That they all may be one. Then the promotion of unity is set forth by a pattern of unity, when He says, as Thou, Father, art in Me, and I in You, that they also may be in Us, so that as the Father is in the Son and the Son in the Father, so through the pattern of this unity all might be one in the Father and the Son.
Source: On the Trinity (New Advent)