The sermon on the mount is similar to the OT commandments. It gives the plan for being a good Christian by showing what God's standards are. Way over and above anything we can do. In that vein you can see that beyond faith and trust, Christ shows that he does want us to attempt to adhere to the law, even if we cannot follow it perfectly. It's still a good roadmap on how to live well and make life good for everyone. If society would fall back on that, you'd see a lot less of the issues that we currently face.