I've argued that the Bible gives us two different classes of texts with respect to eternal life. One class reveals that eternal life already belongs to the believer. Another class shows that eternal life is something that is yet future. How can both of these things be true? One way of explaining the already/not yet of eternal life is quantitative. That is, we might simply say that the believer already experiences some of eternal life, but has yet to experience the fullness of eternal life. While that is true, there is a more fundamental, qualitative distinction to be made.
A Present Possession (Objective)
The biblical terms used to describe the believer's current relationship to eternal life imply possession or ownership. The believer "has eternal life" (Jn 5:24; 6:47). This possession or ownership of eternal life is something God gives to those who are His (Jn 10:28; 17:2). It is a free gift (Rom 6:23), which means it is not merited or earned by those who receive it. The possession of eternal life is granted to the elect, to those who were chosen in Him eternally, and it is granted to them at the moment they first believe (Acts 13:48). We can never earn eternal life so as to buy it for ourselves by our own works of obedience to the law (Gal 3:21). Rather, eternal life was purchased by the righteousness of Christ in His life, death, and resurrection (Rom 5:18, 21) and bestowed freely upon all in whom the Spirit works regeneration and faith.
A Present and Future Experience (Subjective)
Eternal life is something that believers experience or enjoy in the present at the moment they first believe. However, the full enjoyment and experience of eternal life is yet future and contingent upon perseverance and transformation into the likeness of Christ (which transformation is always manifest by good works). If you lose your [temporal] life, you will find [eternal] life (Matt 10:39). Those who inherit eternal life in the future are those who in this life turned from the world to Christ (Matt 19:29). Those who do righteous deeds gain access to the experience eternal life in heaven (Matt 25:46). Rom 6:22 teaches that the outcome of sanctification (i.e., perseverance) is eternal life. The Bible says that we have to fight in order to experience and enjoy eternal life: "Fight the good fight of faith; take hold of the eternal life to which you were called" (1 Tim 6:12). Revelation 2:10 says, " Be faithful until death, and I will give you the crown of life."
Possession. My little girl and I have a relationship. She is my daughter. She did nothing to earn her status of "daughter." She was simply born into my home freely. Nothing that she does will be able to make her "not my daughter." Her "daughter" status is utterly unconditional. She is permanently and unconditionally in relationship with me.
Experience. However, for my daughter to enjoy our relationship, she must obey me. That's because if she does not obey me, I will make sure that she doesn't enjoy our relationship. A happy daughter is an obedient daughter. But, if she disobeys, I will lovingly and graciously discipline her, removing from her the enjoyment of our relationship, so that she might enjoy it more at a later date. The enjoyment and experience of our relationship is contingent upon her works.
Similarly, God, who is eternal life, gives us Himself freely. But, for us to enjoy Him, we must become like Him and obey Him. An unregenerate man who entered into heaven would not enjoy it. Indeed it wouldn't seem like heaven at all. In order for us to experience what is truly heaven - God Himself, we must be glorified, made into the likeness of Christ, or else we would never enjoy Him.
Put differently, Christ's objective righteousness alone makes us morally or legally fit for heaven (justification). But our subjective righteousness makes us naturally or ontologically fit for heaven (sanctification).