Theophylact of Ohrid
Catena Aurea · Johannesevangelium 1
He came unto his own, and his own received him not. But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name: Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
Or the meaning is, that the most perfect sonship will only be attained at the resurrection, as saith the Apostle, Waiting for the adoption, to wit, the redemption of our body. (Rom. 8:23) He therefore gave us the power to become the sons of God, i. e. the power of obtaining this grace at some future time.