Eternal life is freely given to all who ask by having saving faith in Him. The first century Christians wrestled with this as well. Look at Romans Chapters 5 and 6. Paul is responding to believers who said that if Christ brought forgiveness for sin, why should we stop sinning. We were therefore buried with him through baptism into death in order that, just as Christ was raised from the dead through the glory of the Father, we too may live a new life.
Lets start with a short look at what saving faith encompasses.
Saving faith is a combination of the exercise of our free will, the truth of Christ's message, and the operation of the Holy Spirit in our heart. Therefore we need not fear that this faith we speak of is beyond our ability. Already the Holy Spirit is working to produce saving faith in all who ask. Remember that it is not behaving differently that makes us a Christian, but being a Christian makes us behave differently. Saving faith will produce a change in our life now, not just on judgment day.