A brief piece of writing I composed on a fundamentally important question.
John the Baptist spoke in Luke 3:9, "The axe is already at the root of the trees, and every tree that does not produce good fruit will be cut down and thrown into the fire." Lack of good fruit is proof of a fatal condition in a man's heart. We all tend to brush over such verses carelessly. The reason for this is that God causes fruit to spring forth in the lives of all Christians. We know this because all Christians have the Holy Spirit helping them daily become sweeter and sweeter. And since we are Christians we must have this fruit. We as Christians, however, should check to see that we truly are bearing good fruit. For we may be being deceived by the devil.
Jesus speaks of this deception in Matthew 7:21-23: "Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but only he who does the will of my father who is in heaven. Many will say to me on that day, Lord, Lord, did we not prophesy in your name, and in your name drive out demons and preform many miracles?' Then I will tell them plainly, I never knew you, away from me you evildoers." This passage should be of great concern for us for Jesus speaks of this group as consisting of many.' These people surely displayed what looked like good fruit and yet they were thrown into the fire for lack of it. For this reason we need to contemplate deeply what truly constitutes good fruit, so that none of us will be thrown into the fire of hell because we were deceived by the devil and our wicked hearts into believing we were saved.
How does a person know if they have good fruits? John the Baptist spoke that the fruits must be good, not any old fruits will do. How can we be sure that the fruits we see showing up in our lives are not the fruits similar to a kind and generous atheist. For our fruits may well look good by human standards, but how can we know that they are the kind that flow from the Holy Spirits infusion of Christs righteousness into our lives. I believe that the answer can be found in our attitude toward God. God demands from us all to love him with all our heart, mind, soul, and strength. We on earth will surely never be able to give him this, but if Christ's righteousness is being given to us in increasing measures we will surely see strides as our love grows for God.
If we see our love for Christ growing daily this will be a sure sign that we are saved. But, if our love to Christ is very similar to what it was five or ten years ago we should begin to wonder what is going on in our lives. In Jesus's parable of the sower the good see that produced fruit multiplied thirty or sixty or even a hundred times. Since the Christian life is meant to multiply in such terms faith that multiplied but a very small crop must be examined carefully. Those who the spirit is creating fruit in will naturally have a greater desire and love for God.