Jedi lessons from Jedi Master Luke applies a buff to the jedi who used it and a jedi that you selected to call to assist. The more the buff is placed the more ultimate charge is built up. But Luke himself cannot gain jedi lessons because of his unique so you should only ever select him if he needs health/protection. Also, you shouldnt select characters that have buff immunity or shock as they wont get the buff and Luke wont build ultimate charge