Lord Tobias said:
still does not answer my question
How does it not answer your question? In Empire Strikes Back, Vader reveals to Luke that he is his father. He asks Luke to join him so they can overthrow the emperor and rule the galaxy as father and son. It is a temptation.
In Return of the Jedi, the Emperor and Vader goad Luke into using the dark side of the force. They are both dark side guys. They like the dark side. It is another temptation.
Just as Vader thought surely my son is going to join me and sign up to rule the entire galaxy when he tempted Luke in the previous movie, these two dark side guys who love the dark side, would have believed that Luke would fall in love with the dark side once he used it, just like they did, and he would become one of them.