You're right; the world would be a far better place if everyone put Jesus' teachings into action. Think, for example, how different the world would be if everyone obeyed the Bible's command to love others just as much as we love ourselves (see Romans 13:9).
Tragically, however, the Bible does not promise that this will ever happen -- not until Christ comes again to rule over the world in perfect justice and peace. In fact, the Bible indicates that as time goes on, evil will continue to grow as Satan lashes out against God and His people. But God's work will continue to grow also, until the final judgment brings an end to the conflict.
Do you remember Jesus' parable about a farmer whose enemy sowed weeds in his field? (You can read it in Matthew 13.) Over time, the wheat and the weeds grew up together, and only at harvest time were they separated -- with the weeds being burned. This, Jesus said, is an illustration of our world, with both good and evil growing together until the end of time.
Should this make us throw up our hands in despair, saying it's useless to tell others about Christ's salvation or try to make the world a better place? No, not at all! God is still working -- and so should we. Never forget Jesus' words to His disciples: "As long as it is day, we must do the work of him who sent me. Night is coming, when no one can work" (John 9:4).