The parable of the weeds and the wheat is exactly that a parable, and not an allegory. In a allegory, characters and objects represent specific ideas on a one to one basis. Parables are different because there are multiple levels of meaning.
Today's parable can rightly be looked at as a reference to how God's leniency, mentioned in the first reading, works. While the servants want to rip out the weeds immediately, in our modern language "swift justice." The master tells them to wait for harvest time. For us this is a clear symbol of the last judgement, the final separation into heaven and hell.
But there is another level on which we can look at this parable and this brings us back to the topic of purgatory. If we look at the parable on a personal level, we all have within us both wheat and weeds. There are within all of us, attitudes, feelings, prejudices, old injuries, thoughts and feelings that we should not have, and can not take with us into heaven.
This parable reminds us that at the time of the harvest, god will not only separate the good people from the bad. He will also reach into each of our hearts and separate the wheat from the weeds, cleansing us of everything that is not good and holy, everything that is not love. We will finally be truly free, purged of every impulse that keeps us from being the person God created us to be. With the weeds removed when can then spend eternity falling ever more deeply into the love that is God. This final weeding we call purgatory, and eternity in God's presence we call heaven.
Perhaps as a part of today's Sabbath it might be good for each of us to look into our hearts and do some weeding ourselves. Can we start by identifying the weeds? Or perhaps we need to take a step back, and ask God to help us to see the weeds we cannot see, the ones that travel under the surface. If we do not tend the spiritual garden of our heart, the weeds can and will take over.
Today is a good day for gardening.