Alcuin: And because all things are in His hand, the life everlasting is too: and therefore it follows, He that believes on the Son has everlasting life.
Bede: We must understand here not a faith in words only, but a faith which is developed in works.
Chrysostom: He means not here, that to believe on the Son is sufficient to gain everlasting life, for elsewhere He says, Nor every one that said to Me, Lord, Lord, shall enter into the kingdom of heaven. And the blasphemy against the Holy Ghost is of itself sufficient to send into hell. But we must not think that even a right belief in Father, Son, and Holy Ghost, is sufficient for salvation; for we have need of a good life and conversation. Knowing then that the greater part are not moved so much by the promise of good, as by the threat of punishment, he concludes, But He that believes not the Son, shall not see life; but the wrath of God abides on him. See how He refers to the Father again, when He speaks of punishment. He said not, the wrath of the Son, though the Son is judge; but makes the Father the judge, in order to alarm men more. And He does not say, in Him, but on Him, meaning that it Will never depart from Him; and for the same reason He says, shall not see life, i.e. to show that He did not mean only a temporary death!
Augustine: Nor does He say, The wrath of God comes to him, but, abides on him. For all who are born, are under the wrath of God, which the first Adam incurred. The Son of God came without sin, and was clothed with mortality: He died that you might live. Whosoever then will not believe on the Son, on him abides the wrath of God, of which the Apostle speaks, We were by nature the children of wrath.