"He who sows good seed is the Son of Man," Jesus explains to His disciples, "the field is the world, the good seed the children of the kingdom. The weeds are the children of the evil one, and the enemy who sows them is the devil."
That's the world in a nutshell, right? The good and the bad, side by side.
It's also the Church. The good and the bad, side by side.
It's also each of us. The good and the bad, side by side. We each bring forth good deeds begotten by God, and also evil deeds begotten by the devil.
It's also many of our individual acts. The good motive and the bad, side by side.
The eschatological perfection of the world this parable foretells may also explain why God doesn't seem eager to make us perfect as He is perfect. As it is the nature of a seed to grow into a fruitful plant, so it is the nature of a human to grow into a perfect child of God, and forcefully uprooting the weeds in our nature -- weeds, let us not forget, that we ourselves have nurtured -- may also uproot the good plants through which we are to be perfected.