Full Text of the 17th Amendment
The Senate of the United States shall be composed of two Senators from each State, elected by the people thereof, for six years; and each Senator shall have one vote. The electors in each State shall have the qualifications requisite for electors of the most numerous branch of the State legislatures.
When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies: Provided, That the legislature of any State may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.
This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution.
The original system of having state legislatures elect U.S. senators began to break down with the growth of political parties in the mid-19th century. Disagreements between and within parties produced deadlocks that delayed state legislative business and left states without their full Senate representation, often for lengthy periods. This amendment provides for senators to be elected the way members of the House are—by direct election of the people. Source: U.S. Senate
Popular Election of Senators: Under Article I, Section 3, two senators from each state were elected by the legislature of each state. Under this scheme senators represented the states to the federal Union, and members of the House represented the local voters in their district.
But a series of scandalous elections and widespread political infighting in state legislatures, led Progressives to call for the election of senators by voters of each state. Ratified by the states in 1913, the Seventeenth Amendment provides that senators be elected by the people directly. Source: Annenberg Classroom