Luke is brandishing the Skywalker saber instead of his green one. This is of great symbolic importance. After refusing the saber - symbolizing the identity of the Skywalkers - twice, he is finally shown to have accepted it. Rey has shown him Vader is not the family’s true identity and she has both taken it upon herself and will reforge it (without even knowing it). At the same time, Luke taunts Kylo with the blade, showing the future of the family does not lie with him.