"Under the U.S. Constitution, the legislative branch enacts the laws, the executive branch enforces the laws, and the judicial branch interprets the laws. Why is this separation of governmental power important?"

The seperation of governmental power to legislative branch, executive branch and judicial branch is important to avoid corruption. If those three powers would not be splitted, someone could use those powers to his own advantage. If the legislative branch and executive branch would be combined to one branch, the people who would make laws would be the same people who would enforce them and that would cause injustice.

The legislative, executive and judicial powers have to be seperated, otherwise there would be a greater possibility for one person or group to capitalize those powers for their own wills. The powers are divided to protect the values of the country and to illuminate the chance to have all branches under one power, which could end as a dictatorship.