The main reason why we can be sure of the present actuality of eternal life, as sure as we are sure that we are alive today, is the one and only Savior God has provided. Indeed there is no other way to life but through the atoning suffering of the Lord Jesus. It is sufficient; it is acceptable. If the Son of God were to fail, there would have been no life, and there would have been no God in the first place. Salvation is as sure as the reality of God.