Jesus, the Revelator admonished the faithful Smyrna church in Rev. 2:10, “Be faithful until death, and I will give you the crown of life.” At first glance, remaining faithful may seem simple. However, the church at Smyrna was being severely persecuted. They were to remain faithful even if it cost them their physical life. That makes being faithful not so simple.
The first Christians shared their goods with the poor. They were zealous in preaching/teaching the gospel to others. When persecutions arose, they went elsewhere continuing to preach the good news of salvation. They practiced what they preached.
Jesus said in Mt. 5:16, “Let your light so shine before men, that they may see your good works and glorify your Father in heaven.” Even though that was not spoken to Christians, it applies to Christians as well.
Peter summarized fruitful Christian growth in II Pet. 1:5-11 when he wrote, “But also for this very reason, giving all diligence, add to your faith virtue, to virtue knowledge, to knowledge self-control, to self-control perseverance, to perseverance godliness, to godliness brotherly kindness, and to brotherly kindness love. For if these things are yours and abound, you will be neither barren nor unfruitful in the knowledge of our Lord Jesus Christ. For he who lacks these things is shortsighted, even to blindness, and has forgotten that he was cleansed from his old sins. Therefore, brethren, be even more diligent to make your call and election sure, for if you do these things you will never stumble; for so an entrance will be supplied to you abundantly into the everlasting kingdom of our Lord and Savior Jesus Christ.”
Christians may know that they are still saved if they are continuing to walk in the light. John wrote in his first letter, “But if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ His Son cleanses us from all sin” (I Jn. 1:7). The word “cleanses” indicates a continuous action that removes sins as they occur in the lives of faithful Christians. However, that is not a license to refuse to repent of those sins (Rom. 6:1-23).