I believe that the SCJP certification itself is a motivation for studying Java. In fact, that's how it is in my case. I was not having a enough motivation and there was no direction when I started to learn Java. Since Java is so vast, you can easily get lost as to where to start and what to learn. SCJP gave a very good direction and a goal. Plus when you are working and have a family it's easy to forget/ ignore to study with your busy schedule.
But since the time I decided to do SCJP, I am finding that I am studying every single day without fail.
Then when I came to Javaranch forums, it's inspiration everywhere This place is filled with energy. And the stories in the results forum also motivates you a lot.
When you get into the flow, I think you will get your motivation, the important thing is to just start it and not keep thinking that I will do it when I have more time or when I finish my current activity etc. etc. Wishing you all the best!