In Acts 17:24-34 we get to hear a sermon that Paul preached to philosophers in Athens. He presented to them biblical truths about God, humans, Jesus, and our response. The game-changing declaration that got Paul laughed off stage was the resurrection of Jesus. The news about the resurrection left others curious enough to want to hear more, some of whom ended up believing the gospel message. That gospel is the same today, as relevant to us as it was to those philosophers, and life-changing good news to any who will believe it.
In the earlier parables, Jesus left people wondering what he meant. In the latter parables, Jesus was often very direct. For example, in Matthew...
While the Old Testament is still valid, we also have the message of the one who was raised from the dead.
God gave us The Ten Words, which show us how to live well and our need for Jesus Christ.