Why did Luke choose to disappear?

Why did Luke choose to disappear, when he could have easily subdued Kylo Ren? Why did he choose to remain hidden, when he knew that the First Order was such a big a threat? Was he afraid that he will also succumb to the Dark Side when revenging the padawans?

This issue will certainly be addressed in Star Wars: Episode VIII. Furthermore, it is expected for the answer to be delivered on the same island where he is found, since Mark Hamill has already shot a scene for the sequel in the same surrounding.

But the safest bet is that he was also tempted by the Dark Side and he removed himself from the scene.