How we cite our quotes: All quotations are from Star Wars: Episode VII - The Force Awakens.
Quote #4
REN: And Han Solo. You feel like he's the father you never had. He would have disappointed you.
Daddy issues alert. Ren is motivated in large part because his father let him down. We're not privy to the reasons, but when dad's a career criminal with a habit of stepping out on his responsibilities, you can make an educated guess.
In response, Ren turns to another relative for inspiration: his grandpa.
Quote #5
REY: You...you're afraid...that you will never be as strong as...Darth Vader!
That mental interrogation thing works both ways, doesn't it, Ren? Rey pulls Ren's dark, dirty secret out of him and sheds a whole lot of light on why Ren is doing what he's doing. Daddy let you down, look to the elder generation to provide a path. (The irony, of course, is that Darth Vader eventually renounced the dark side and was redeemed. That may explain why Ren may have some conflicted feelings…)
Quote #6
REN: Forgive me. I feel it again. The pull to the light. Supreme Leader senses it. Show me again the power of the darkness, and I will let nothing stand in our way. Show me, Grandfather, and I will finish what you started.
It's interesting that, while Ren has completely abandoned his living family, he still clings to his dead gramps in order to feed his power. Seems he's not comfortable going it completely alone, and he still needs some contact with his family after all.