The best explanation of President Andrew Jackson's statement, "[Chief Justice] John Marshall has made his decision, now let him enforce it!" is: The Supreme Court does not have the power to enforce its decision, so President Jackson could ignore it.
This statement reflects Jackson's belief that the executive branch, led by the president, was responsible for enforcing laws and decisions, and that the Supreme Court lacked the means to enforce its rulings without the cooperation of the executive branch. In the context of Worcester v. Georgia, Jackson's response indicated his unwillingness to support the court's decision in favor of the Cherokee nation against Georgia's laws.