It is a great question. And that is because many people don’t want to think about whether they have done what they should have done in life. For many centuries the church has argued over the doctrines of salvation. For most of us we have settled our minds on one way of looking at salvation and have completely discarded all other theories. I think that’s a problem. If you have decided that “once saved, always saved” is the only true way to look at it, then you may be making a mistake. If you have decided that “works righteousness” is the proper teaching of the Church, then where are you putting your faith? You and I should not live in a state of relative certainty about such important issues. But that is where we are more comfortable in this life. We should be constantly asking the question, “what if I am wrong?” Most assuredly a big chunk of Christians are going to be found to have lived life trusting in the arguments of theologians rather than trusting in the grace of God.
That is where the genius of this question comes into play. In the Gospel of John, Jesus tells us that our fruitfulness is dependent upon Abiding in Jesus. Here is the passage: (John 15:1-6) I am the true vine, and my Father is the vinedresser. 2 Every branch of mine that does not bear fruit he takes away, and every branch that does bear fruit he prunes, that it may bear more fruit. 3 Already you are clean because of the word that I have spoken to you. 4 Abide in me, and I in you. As the branch cannot bear fruit by itself, unless it abides in the vine, neither can you, unless you abide in me. 5 I am the vine; you are the branches. Whoever abides in me and I in him, he it is that bears much fruit, for apart from me you can do nothing. ESV
As far as knowing how fruitful we have been is concerned, that is none of our business. It is God who makes us fruitful, not ourselves. We have responsibility for seizing opportunities, but our words and our deeds are given us by the Holy Spirit. In my opinion, what is necessary for being a faithful Christian is abiding in Christ. What that means is living with Christ as a close and cherished relationship. This is a lot like a good marriage. I know of celebrities where one member of the couple lives in New York and the other lives in Los Angeles. That distance does not make for a good marriage. It is possible to craft a good marriage out of that situation, but it requires a great deal of effort to overcome the distance. Abiding in Christ is a lot more than a warm and fuzzy feeling about Jesus. Abiding means to “live with”. It consists in building a life with Jesus as your constant companion. It means talking with him. Seeking advice from him. Drawing comfort from him. Abiding means more than just living in his neighborhood, it means sharing in his life.
If you abide with Christ and make him a part of your everyday life, you can be assured that you will be productive because he will make you productive. If you choose to live apart from him, living with him in your neighborhood and not in the intimacy of your heart, then you may do many of the things that you want to do, but you will have no idea what he wants you to do. And that’s the fruitfulness that counts.