The statement "[Chief Justice] John Marshall has made his decision, now let him enforce it!" reflects the idea that the Supreme Court's authority is limited to interpreting the law and that it relies on the executive branch, led by the president, to enforce its rulings. Therefore, the best explanation of this statement is:
The Supreme Court does not have the power to enforce its decision, so President Jackson could ignore it.
This highlights President Jackson's stance that he did not feel bound by the Supreme Court's ruling in Worcester v. Georgia, which favored the Cherokee Nation's rights.