Jesus answered and said to him, "Truly, truly, I say to you, unless one is born again he cannot see the kingdom of God." (John 3:3, NASB)
As I mentioned earlier, justification is not the whole story. There is another idea in Scripture, new birth. Justification saves us from the punishment or penalty our sins deserve before God: it is the acquittal God hands down that guarantees our sins will never be brought up by God to condemn us. But new birth is fundamentally different: it gives us eternal life. Justification is a legal idea, new birth is an organic idea.
I've already mentioned that the epistles protray us in various states of death, burial, and resurrection; all following the path of the Son of God, "who was declared the Son of God with power by the resurrection from the dead, according to the Spirit of holiness" (Romans 1:4, NASB):
- Ephesians protrays the unregenerate as dead in sins (Ephesians 2:1), and the believer as raised with Christ (Ephesians 2:5), ascended with Him into Heaven, sitting with Him at God's right hand (Ephesians 2:6).
- Romans presents the unregenerate as very much alive in sins (Romans 1:18--31), the believer as crucified with Christ, buried with Him, and raised with Him (Romans 6:3, 4).
- Galatians presents the believer as dead to the Law, but now living to God (Galatians 2:19); crucified with Christ, but now living in His power (Galatians 2:20); and crucified to the world (Galatians 6:14).
- Colossians presents the unbeliever as dead in sins (Colossians 2:13), the believer as buried with Christ, and raised with Him (Colossians 2:12).
As a side note, I've met a lot of Christians who built their entire theology around the idea that unbelievers are "spiritually dead", as in Ephesians. But a simple glance at Romans indicates the Scripture also contemplates unbelievers as very much alive in their sin.
John's Gospel presents the Lord Jesus as the one who brings life to the dead (John 5:25--29). This is not exactly the same idea as the resurrection with Christ in Romans, Ephesians, and Colossians; but I think it is closely related. John's Gospel discusses the unregenerate as needing an entirely new life in order to be part of the new creation. So John 3 includes the famous discussion with Nicodemus, where the Lord Jesus tells him he needs to be "born again" in order to enter the kingdom of God. John 4 includes the discussion with the woman at Sychar, who needs to drink "living water". John 5 presents the Son of God who will call forth the dead in two resurrections: one for the just, one for the unjust (John 5:29). John 6 centers on the Son of God who is the Bread of Life that came down from Heaven to give life to the world (John 6:33); and the one who eats this bread will neither hunger nor thirst (John 6:35).
Eternal life, like justification, is not something we earn, but something God gives to the one who believes: "For this is the will of My Father, that everyone who beholds the Son and believes in Him will have eternal life, and I Myself will raise him up on the last day... Truly, truly, I say to you, he who believes has eternal life." (John 6:40, 47; NASB).
I want to keep eternal life and justification distinct, because Scripture does. But I maintain that the one who is justified also has eternal life. God gives both justification and eternal life to the sinner who believes. And I refuse to be drawn into an argument about which one happens first.
But eternal life carries implications that justification doesn't. Justification implies no change in the justified: he doesn't stop being a sinner just because he has been acquitted! But eternal life absolutely implies the recipient is changed. How could he not be? He used to be dead, now he is alive.
If you are a believing sinner, you are acquitted: you are free to go your way, and God will never condemn you for your sins. But if you have been given eternal life, then you have in fact been changed. This now implies some things about your new life. This is where we see the question "What about the fruit?".
The first implication is, you need to feed the eternal life. Eternal life, by definition, can't end in death. But just like the natural person has a life that needs to be fed, the child of God has an eternal life that needs to be fed. The Lord Jesus discusses this in John 6:50--58. Jesus declared Himself to be food that gives eternal life. The believer receives this eternal life from Him in v. 47. But then He gives eternal life to the one who feeds on Him in vv. 55--57. The first eating in v. 35--40 is a one time deal: believe, and you have eternal life. But vv. 55--57 reveal something a little different: continue eating---feeding---to sustain your eternal life.
The Lord Jesus declared Himself to be the one from Heaven to give His flesh to us as food and His blood to us as drink. Contrary to Roman Catholic theology, I don't consider this a reference to the Lord's Supper. It's not the actual bread and wine of the Lord's Supper that gives us eternal life. But then, the Lord's choice of bread and wine for the Lord' Supper is certainly a reminder of this passage.
The Lord's offering us His flesh and His blood implies His death. And it is exactly as we feed on Him as the One who died for us that our eternal life is sustained.
How do we do that? Well, I'm not sure I have a complete answer. But I would suggest we start with a constant remembrance of the One who died for us. I would suggest this includes constant Bible reading and study, prayer, and meditation.
I suggested before that trying to force-grow fruit results in tasteless fruit. But keeping the tree from which the fruit grows nourished and healthy has the opposite effect. When a Christian is pressured or panicked into producing "fruit", it tends to be of inferior quality; if it is actually "fruit" at all, and not merely the offering of the flesh within him. But when a Christian invests time and effort into the Word of God, prayer, meditation: when he feeds on Christ, then the fruit he produces is of an overwhelmingly superior quality.
but we preach [a] Christ crucified, to Jews a stumbling block and to Gentiles foolishness... For I determined to know nothing among you except Jesus Christ, and Him crucified. (1 Corinthians 1:23, 2:2; NASB)