"How can I know eternal life?" Shouldn't the question be, how can I have eternal life? Isn't salvation something believers possess?
"Have" would work in the title. After all, the sure promise of eternal life is precious to those who have trusted in Jesus Christ. The joy of sins forgiven stands as a gift, offered from the gracious hand of God to all who will repent and believe. Removal of sin's guilt that renders us odious before a holy God, deliverance from sin's power that pulls us down into the pit of hell, provision of the cloak of spotless righteousness earned on our behalf--the gospel of life in Jesus Christ contains all these. That gospel is a gift and the hope of its recipients stands as a present possession.
Yet the gospel is more. It brings something greater than a treasure trove of gifts. It brings us the Giver Himself. In His high priestly prayer recorded in John 17 that showcases the glory of the gospel and the personal involvement of God in all its facets, Jesus surprises us with His description of eternal life.
"And this is eternal life, that they know you the only true God, and Jesus Christ whom you have sent." (v. 4)
Eternal life involves not just having. It reaches to the redemptive heights of knowing God, knowing Him in restored, reconciled relationship. The Christian life embarks on the journey of growing in the grace and knowledge of this God, where goodness and mercy follows us all the days of our lives and we will dwell in the house of our God forever, not as guests but as His children, not temporarily but for eternity.