Ephesians 1:13-14 In whom ye also [trusted], after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise, Which is the earnest of our inheritance until the redemption of the purchased possession, unto the praise of his glory.

After being regenerated; after being adopted as a child of God; after having been given the greatest inheritance of eternal life; if the person will put his trust in this gospel message and then believe, he will receive the earnest (a small amount provided in advance) of the same inheritance that he obtained at adoption, which is reserved in heaven. This earnest of eternal life and eternal salvation is for the present. This is taking possession of life and salvation now. This is the life that the person will have while in obedience to God, and the life he will loose if he is disobedient. This is the salvation he finds, if he is obedient to God, and the salvation he will loose unto destruction, if he is disobedient to God. The earnest which a person receives for obedience is the only part of the inheritance a person can loose, or fall away from, no matter how great the sin, because our inheritance in heaven is given by grace, and not by works of righteousness.