John 6:40

Faith, so to speak, is the attempt generated in time; the final result is the attainment of the promise secured for eternity. Now the Lord himself has most clearly revealed the equality of salvation when he said, "This is indeed the will of my Father, that all who see the Son and believe in him may have eternal life; and I will raise them up on the last day." As far as possible in this world, which is what he means by the last day—and which is preserved till the time that it shall end—we believe that we are made perfect. Wherefore he says, "The one who believes on the Son has everlasting life." If then, those who have believed have life, what remains beyond the possession of eternal life? Nothing is lacking in faith as it is perfect and complete in itself.

He has said two things: "This is the work of God that you should believe in the one whom he has sent," while here he added, "whoever sees and believes." The Jews saw but did not believe; they had the one condition, lacked the other. How could they attain to eternal life without the other? The reason those who saw did not attain eternal life was because they did not also believe. If so, what about us who have believed but have not seen? If it is those two things that earn eternal life, seeing and believing—and whoever is lacking one of them cannot attain to the reward of eternal life—what are we to do? The Jews [who saw him] lacked the one; we the other. They had seeing but lacked believing. We have believing but lack seeing. Well, as regards our having believing and lacking seeing, we have prophetically been declared blessed by the Lord himself just as Thomas, one of the Twelve, was blessed when he felt his scars by touching them.

(Tr. xxv. 19) See how the twofold resurrection is expressed here. He who cometh to Me, shall forthwith rise again; by becoming humble, and a member of Me. But then He proceeds; But I will raise him up at the last day. To explain the words, All that the Father hath given Me, and, I should lose nothing, He adds; And this is the will of Him that hath sent Me, that every one which seeth the Son, and believeth on Him, may have everlasting life: and I will raise him up at the last day. Above He said, Whoso heareth My word, and believeth on Him that sent Me: (c. 5:24) now it is, Every one which seeth the Son, and believeth on Him. He does not say, believe on the Father, because it is the same thing to believe on the Father, and on the Son; for as the Father hath life in Himself, even so hath He given to the Son to have life in Himself; and again, That whoso seeth the Son and believeth on Him, should have everlasting life: i. e. by believing, by passing over to life, as at the first resurrection. But this is only the first resurrection, He alludes to the second when He says, And I will raise him up at the last day.