The framers gave the federal government the ability to change (aka amend) the Constitution over time. The ability to add in new amendments is one of the many factors that helps this document to stay relevant.
Besides the ability to change the constitution, the ability to interpret what the constitution means helps as well. For example, the judicial branch of the federal government has the power of judicial review. This allows the court to interpret whether or not federal laws violate the constitution. This ability to consistently interpret what is constitutional and unconstitutional makes the constitution an adaptable set of laws.