John 3:16

For God so loved, &c. This is said by way of anticipation, lest Nicodemus should object, "If thou art the Son of God, how will God suffer Thee to be suspended and exalted upon the cross?"

Christ meets this by implying that God will permit it in order to show forth His burning love to men, which was typified by the serpent of brass, which is called in Hebrew saraph, which means fiery, and setting on fire. So S. Chrysostom and Theophylact.

Observe that every word of Christ in this sentence has a great and special emphasis, in order to magnify to the utmost the love of God. For (i.) He says, So, with such vehemence, such excess of love. 2. Not a king, or an angel, loved, but God. 3. Loved, i e., first and as it were gratuitously; without merit, yea, even without desire on our part. 4. The world, His enemy, and under the sentence of damnation. 5. Gave not another man, not a. angel, not another world, but His Son; and that not an adopted Son, but His own Son; and again not one Son of many, but His only Son, His Only Begotten Song of Solomon 6. He did not sell, or lend, but gave freely; and not to a kingdom and triumphs, but to death and the Cross. 7. Christ did not do it for Himself, to gain any advantage for Himself, but that He, the Creator, might give life to us His creatures by His own death, that by His humility He might exalt us, that by His emptying Himself He might heap upon us eternal glory, and an infinite weight of wealth and goodness. This is the love of God towards man, which the Apostle celebrates (Tit 3:5).

You may say, it would have been greater love if God the Father had given Himself for us, and taken our flesh, than that He sent His Son. For he gives more who gives himself than he who sends another.

But I reply that this is true of those who are of a different essence, but not of God: for the Father and the Son have the same Divine Essence, and are consubstantial. Wherefore the Father, in giving us His Son, with Him gave us His own Essence, than which nothing greater can exist, or be given. This gift of the Father was therefore the greatest possible, and infinite. So S. Cyril on this passage.

You may further urge, God gave not His own Person, but His Essence only: and that He would have given more if He had given His Person also. I answer by denying the conclusion. 1. Because Person is God is in reality the same as Essence; for it adds nothing to His Essence except relatively, and the idea of distinction from the other Persons: also because the Person of the Son is as worthy a the Person of the Father. For all the three Divine Persons are co-equal in all things, as the Athanasian Creed saith. Besides, the Father in giving the Person of His Son, gave us also His own Person, as well as the Person of the Holy Ghost. Because the Father is in the Son, and both are in the Holy Ghost. And again the Son is in the Father, and the Holy Ghost in the Father and the Son, of which I will speak more fully on chapter xiv. 10.

Moreover S. Thomas (3 part, qu. 3) gives several reasons why God the Father gave not proximately His own Person, but the Person of His Son; or why the Son alone took upon Him our flesh. Among which the primary is, because the Father willed to adopt us and our nature, and to make us His sons, and so heirs. For He made His Son to be our brother, that by Him we might become sons of God, and so heirs, as Christ here intimates.