Your villain needs two more streets to get his money in, possibly because he's on a draw. You're telling him with this raise that more money is going to come flying at him on the turn and that you want to get your stack in. Is his hand strong enough? You're effectively risking 1/4 of your stack to put him to a decision for all of his chips, which tends to lead to a guessing game, which tends to lead to wrong decisions.

Tell me how close I was. :P