We can know that we are on the way to heaven if we have faith in Christ (John 6:47). This faith has two parts.
The first part of this faith is a confident assurance that what Jesus says about how to live life is true (John 3:12). This assurance brings us knowledge that we have not, even for one moment, lived free from sin. We have done things that Christ tells us not to do or failed to do things that Christ tells us to do. This knowledge of the right path leads to repentance, turning from our sins to God and His way of living.
This faith is also an assurance that Christ paid the penalty for our sins. Not just for sins in general, but for our sins in particular.
Christ is God who became a man. He laid aside His rights and abilities and came to earth. He lived a perfect life. This life is an example to us, but it also gives Him credit for a life lived in perfect obedience to God’s law. He then died on the cross for us. In some way know only to the God of all, Christ took the credit for our sins and suffered God’s infinite, terrible wrath for those sins. He became sin for us that we might become righteous. (2 Corinthians 5:21, Romans 3:21-31)
Faith is the way we take credit for what Christ did for us. The credit for our sins is taken away from us because of His sacrifice, and we are given credit for Christ’s perfect life. The work is outside of us (“extra nos” in Latin). It’s not about what we do; it’s about what is done for us by Christ. When we have faith, the perfect God loves us perfectly because we are credited with perfection. When God looks at us, we are perfect because of what Christ did.
But how can we personally tell if he really believes? How can a person tell if his own faith is genuine? The most useful is Galatians 5:6. It says that what counts is “faith working through love.” Christians do love Christ. Not perfectly; sometimes not even well. R. C. Sproul puts it this way, “I am not asking whether we love this Christ perfectly; I am asking whether we love this God and this Christ at all” (Chosen by God, Wheaton, Illinois: Tyndale House, 1986, p. 166).
We sin, sometimes often. We even sin the same sin over and over. This sin clouds our thinking and convinces us we do not have real faith. But God does not desert us. He always comes to our aid. He helps us to look to Christ and what Christ did for us.
Maybe an old Baptist theologian can help:
The believer in Jesus, who has been regenerated by the power of the Holy Spirit, will never utterly fall away from Christ and be lost. He is not free from temptation; he may, through neglect and failure to employ the means of grace, grieve the Holy Spirit and bring reproach on the himself and the people of
God. He will, however, turn away from his sins and return to his Christian duty; he will not be content in the wayward life. It is the mark of the child of God that he cannot be happy in a life of sin. (E. Y. Mullins, Baptist Beliefs, Chicago: The Judson Press, 1912, p. 53)
The God who saves Christians preserves their faith. He works in Christians to will and to do His will. He does not leave us in life’s battles without a champion.
True Christians will never abandon the faith once and for all delivered to the saints. True Christians can rest confident in their salvation.