Here you go …
This is eternal life: that you know the only true God, and Jesus Christ, whom He sent.
Now before you start questioning this definition, let me share the context and the source of the definition …
After Jesus said this, he looked toward heaven and prayed:
“Father, the hour has come. Glorify your Son, that your Son may glorify you. For you granted him authority over all people that he might give eternal life to all those you have given him. Now this is eternal life: that they know you, the only true God, and Jesus Christ, whom you have sent. I have brought you glory on earth by finishing the work you gave me to do. And now, Father, glorify me in your presence with the glory I had with you before the world began. John 17:1-5 (NIV)
Now certainly there are other dimensions of eternal life explained throughout the New Testament … but this seems to be an all encompassing definition that teaches that eternal life begins in the here-and-now and continues into the hereafter. Eternal life is really about first being known by the Father and Son and in turn then knowing the Father and the Son … all other aspects of eternal life grow out of this foundation!
And this is the testimony: God has given us eternal life, and this life is in his Son. Whoever has the Son has life; whoever does not have the Son of God does not have life. 1 John 5:11-12 (NIV)
May you truly know the one true God and Jesus Christ Who He sent!