A little more about parables. The word comes from the Greek compound word "parabole'." Para means "alongside" and bole' means "to throw." A parable, then, throws something alongside something else, as in yesterday's parable where the Kingdom of Heaven was compared to (thrown alongside) someone sowing good seed.
In the story, someone else came in and sowed bad seed in the field, too. As you heard or read (Matthew 13:24-30, 36-43), there is more to the story, but not enough to make the meaning clear to the disciples. Like those who have to be told why a joke was funny, they ask for an explanation.
Even the explanation, however, can be taken too literally. Parables are ways to jar us into new insights, new thinking. If we require a concrete historical figure or event to attach to the parable, we've pushed it to absurdity. The Kingdom of God is not a field with a farmer and an adversary. For the sake of helping us grasp another tiny insight about it, the Kingdom of Heaven may be compared to a field with a farmer and an adversary.
The gift of parables - the reason we're still reading and wrestling with them today - is that they aren't historical accounts and they aren't absolutist. You don't finish a parable with a definitive, lifelong meaning of "do this, don't do that; be this, don't be that." Each reading, each reflection can help us understand a bit more or a bit differently what God's Kingdom is like and how to be part of it, which, of course, is why Jesus threw those parables out there, so that our thoughts, our lives will be caught up even more thoroughly in his.