Why did God nee to take a rest after finishing His creation?

G-D did not need to take a rest. HE took a rest, because people need to rest up and sleep after working hard. To quote Christ Jesus: "Man was not created for the Sabbath, the Sabbath was created for Man." G-D rested because people need to rest up and therefore as a lesson to humans (created on the 6th day), take a rest and get some sleep after working hard.