16 For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. 
Many years ago, when I lived in Georgia, I participated in a program for one-on-one evangelism that was famous for its two “spiritual diagnostic” questions:
1) If you died tonight, do you know where you would go?
2) If you died tonight, and God were to ask, “Why should I let you in to my heaven?” How would you answer?
Those questions helped many people come to grips with where they would spend eternity and with how heaven was to be gained. They helped my sister-in-law, who was dying of scleroderma; arrive at a dramatic moment of repentance and faith in Christ mere days before she passed over the threshold of eternity. I do not discount them and I’m grateful that I was able to share them with her. But unless someone knows that he or she is dying – and most of us manage to keep ourselves in deep denial over that assured eventuality – a discussion of eternal life feels like just so much esoteric speculation.
In the Bible, however, eternal life is never a matter of obscure speculation. And it isn’t limited to the mere forgiveness of sins and heaven when we die. The most common expression for salvation or the results of salvation, used in the New Testament is: LIFE. (See: Matt. 7:14; 16:25; 18:18; 25:46; John 3:36; 4:14; 5:21; 17:3; Rom. 5:18-21; 6:1-4 for just a smattering of the many references).
That being the case it behooves us to think a bit more thoroughly about the definition of life and then apply what we learn to our understanding of eternal life.
“Life is always and everywhere an inner power to relate to other things in certain specific ways.” 
Life is the power to relate and to interact with the world outside of self. It is the ability to touch and be touched, to see and be seen, and to hear and be heard, among other things. When we stop touching, seeing, and hearing something inside of us dies. Eternal life then, is the power, the inborn ability to touch, to see, and to hear the things of eternity, the things which belong to God.
Life is also the ability to grow and keep growing, to take in from the outside everything we need to develop and maintain our insides. When we can no longer relate to the outside world and draw from it the necessities of life, we die. Eternal life then, is the ability to receive from God everything we need for the life of the soul.
Life is, finally, the ability to pass on life, to yield more life, to produce after our kind. In the natural course of things we lose the ability to bear children. But spiritually speaking, when we can no longer, by communion, and by communication, give life to others we cease to truly live. Eternal life too, presupposes the ability to pass on spiritual life and light. “You are the light of the world,” Jesus said.
What is eternal life? Jesus said it in John 17:3 – “And this is eternal life, that they may know you, the only true God, and Jesus Christ whom you have sent.” It is to be in relationship, now and through eternity, with the life giver, the Living God.