Westcott: New Birth

But in the same Word of God we discover that the known possession of eternal life is the accompaniment of receiving testimony as to Christ. New birth is God's sovereign act, and nowhere does Scripture say, He that believeth shall be born again. To say this would be to take the new birth out of the place in which God has set it, and to make faith in the Gospel antecedent to the new birth. The new birth is an operation in which God is first; for no one can be a co-operator in his own birth. The old Adam does not produce faith, or else those that are in the flesh could please God. It is when sovereign power has broken into our dark night and implanted a new principle of being never there before, that our awakenings and longings, our grief over sin, our breathings after God, can be met, and met only, in Christ. Hence in John 3, where this subject is treated, the Lord Himself when speaking of new birth speaks not of faith. It is only when He presents Himself as lifted up, the Subject of testimony, that He speaks of faith in Himself and eternal life. Nothing of this was presented in the Old Testament as a present blessing. For the Old Testament saint, born again as he undoubtedly was, eternal life was only a promise, and a promise connected with blessing on earth. This blessing, and even the full forgiveness of sins, was to be connected with the fulfilment of the promise of the Messiah. The fear of death was still there, no one was in a position at that time to say that he had eternal life. It is the coming of Christ that has brought life and incorruptibility to light through the Gospel.
It is in the Gospel of John that the present possession of eternal life is so much referred to. And Christ's rejection on earth being anticipatively considered from the very first chapter, eternal life is presented as being secured for God and for the believer in the person of the Son. Hence the oft-repeated statement, "He that believeth . . . hath everlasting life;" and, "He that seeth the Son and believeth upon Him hath everlasting life." The Son was here as the gift of God's love, and in order that the purpose of God for man might be brought to pass. But in order that the love of God might be fully revealed and the whole sentence of death on the first and guilty order of man be carried out and thus annulled for men, He laid down His life as Man after the flesh; then rose again after a new order to which death can never attach, in which He can share with His brethren both His position as a Man before God, and as a Son with His Father (John 20). Let it be remembered that according to the Gospel itself, its own testimony, "these are written that ye may believe that JESUS is the Christ, the Son of God, and, that believing ye may have life in His name." The possession of life (and the known possession of it) flows from faith in testimony.