Many well-meaning teachers proclaim that a true believer will persevere in faith and good works to the end of life. But if one must persevere in faith and good works, then it would be impossible to know that we will end up in heaven. You could never know until the day you died, if you did enough or was faithful enough. And that violates Scripture that tells us we can know (I John 5:13).
This teaching often comes from incorrectly understanding the distinction between justification and sanctification. A person who understands the gospel and believes it is saved immediately from the penalty of sin (Eternal separation from God). Their destiny has changed. They are now destined for heaven. Justification occurs in the court room of God where He pronounces a guilty sinner not guilty. Once you’re saved you can never perish, and no one can snatch you out of God’s hand (John 10:28).
There are numerous examples of people in the Bible who believed and were saved immediately. Someone heard the gospel, they believed it, and they immediately became a citizen of heaven. The Philippian jailer is one example (Acts 16:30, 31). Cornelius, a Gentile, is another example (Acts 10:34-48). At the preaching of Peter, “The Lord added to the church daily those who were being saved” (Acts 2:47).
Sanctification requires perseverance; not justification. If one is to grow spiritually, it will require perseverance. Believers should persevere and not give up. But that is different for every believer. And there are consequences for failing to persevere in faith and good works. But a lack of perseverance will never prevent a born again believer from entering into God’s presence. Learn to discern the distinction and rest completely in the assurance of your salvation by faith alone in Christ alone!