Term limits will free Congress to vote with their conscience, and not be dependent on funding from rich and influential lobbies (such as the NRA) when it is time for re-election.
Why is this important?
Congress too often votes for policies that rich lobbyists favor in order to get them to contribute to their re-election campaigns. Term limits reduces the number of re-elections and the need for re-election funding, stopping Congress from depending on rich donors and lobbyists (such as the NRA) to contribute to their re-election campaigns -- freeing Congress to vote using its conscience.