Theophylact of Ohrid
Catena Aurea · Johannesevangelium 3
For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life. For God sent not his Son into the world to condemn the world; but that the world through him might be saved. He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
(in loc.) As He said above, that the Son of man came down from heaven, not meaning that His flesh did come down from heaven, on account of the unity of person in Christ, attributing to man what belonged to God: so now conversely what belongs to man, he assigns to God the Word. The Son of God was impassible; but being one in respect of person with man, who was passible, the Son is said to be given up to death; inasmuch as He truly suffered, not in His own nature, but in His own flesh. From this deathfollows an exceeding great and incomprehensible benefit: viz. that whosoever believeth in Him should not perish, but have everlasting life. The Old Testament promised to those who obeyed it, length of days: the Gospel promises life eternal, and imperishable.