A person who believes the gospel is immediately delivered from the penalty of sin. He is justified by faith; declared righteous in his positional standing with God. But justification never guarantees that a believer will persevere to the end of life in faith and good works. People teach that; the Bible doesn’t.
The Bible does encourage believers to persevere so that they won’t be barren and unfruitful (II Peter 1:5-8). The writer of Hebrews encouraged them to “not cast away your confidence which has great reward” (Heb. 10:35). They needed to endure the trial which would result in a great reward.
Reward is distinct from a gift. Everlasting life is a gift (Rom 3:23). A gift is not earned. It is freely offered with no strings attached. If there are qualifiers to a gift, it is no longer a gift but an exchange. For example, if I gave you a car and in return required you to give me a ride whenever I need it, the car would not be a gift but an exchange for a service. Gifts cost nothing. However, reward is earned by faithfully following the Lord. Reward is only possible for believers. Unbelievers cannot earn reward because they do not have a relationship with God.
The Hebrew Christians already had “an enduring possession in heaven” that could not be lost (Heb. 10:34). They needed to hang in there to receive a great reward. It would glorify God and be good for them. Since they were already citizens of heaven, they were not being encouraged to persevere so they would go to heaven.
Everlasting life is not a reward for faithfulness. It’s a gift offered freely by God to anyone who believes the gospel. It’s received by faith and last forever. If everlasting life could be taken away, it wouldn’t be everlasting, would it? It would be temporary until you did something that caused God to remove it. And it also wouldn’t be a gift then, if it could be taken away.
As Christians we should encourage one another to hang in there. Life is difficult. God allows trials in our life. We can never grow to spiritual maturity if we give up and quit. You and I can never lose everlasting life, but in the end we will have failed to glorify God if we fail to persevere in the trials of life by faith.