How do you know if you really are a Christian? According to Jesus people are like trees. A tree is known by the fruit that it produces. A good tree produces good fruit and a bad tree produces bad fruit. What is the fruit that evidences whether a person is a Christian?
In Luke 6:45 the fruit is the words that come out of a person’s mouth. And the words that come out of a person’s mouth is inevitable expression of those passions that lie in one’s heart. Out of the overflow of the heart the mouth speaks. You can experience some reassurance that you are a Christian if you love your enemies (reflecting the family likeness of your Father in a task performed only by his Spirit) and if your words reflect a love and joy in the Lord. Both these things encourage us by affirming us that we are in the Lord.
Jesus’ final wisdom parable is about two men who build houses. One builds on a foundation and the other does not. Inevitably the flood waters rise against the house – one remains standing and the other falls quickly and the ruin of that house is great. The point of the parable is that calling Jesus, “Lord, Lord” is not enough. We must build our lives obediently on the foundation of his Word. Flood-like crisis are inevitable but faithful obedience also provides an assurance as we are tested and evidenced to have built well, still standing after the floods of life. But we are also warned that hearing and not doing Jesus’ words will most certainly result in a fall and a great ruin. If we are being disobedient, then we have an urgent need to repent. If we don’t repent and tolerate sin, then our ruin will most certainly come and it will be great.