Our Lord's parables can be applied not just to the Kingdom of God at large, but to us individually. When we hear about the wheat and the weeds in the Gospel this Sunday (cf. Matt 13:24-30) there is a very personal message.
In the parable, the master tells the slave not to pull up the weeds. “Let them grow together until harvest,” he instructs. Sure, the parable informs us about the nature of the Church. The Church has “weeds”—flaws, sinners, and so forth. No field is perfect, and we should not grow too frustrated when confronted with this imperfection. The Church, though holy, will never be perfect.