No law varying the compensation for the services of the Senators and Representatives shall take effect, until an election of Representatives shall have intervened.This seems to be saying that if members of Congress vote themselves a pay raise, the new salaries can’t come into effect until after a congressional election. This looks good because voters would be unimpressed by senators and representatives who’d voted themselves more money — so members of Congress would be less likely to do so, in case the voters turned them out in the intervening election.
However, Congress has gotten around this sensible provision by voting themselves annual cost-of-living adjustments, or COLAs. The U.S. Court of Appeals for the District of Columbia ruled in 2001 that COLAs are not repugnant to the Twenty-Seventh Amendment. The U.S. Supreme Court has yet to pronounce on this question. Watch this space.
The U.S. Constitution's Twenty-Seventh Amendment: Limiting Congressional Pay Raises - For Dummies