Checking for Leaven

Jesus said to them, “Watch and beware of the leaven of the Pharisees and Sadducees.” Matthew 16:6
I always assumed that before packaged yeast became available, most leavening was accomplished with some sort of sour dough. I never cared enough about it to figure out where the sour dough came from. It was just something I would only need to know if the economy collapsed and we had to fall back on old-timey tricks to get by. Happily, creating sour dough starter isn’t rocket science. It is science though.
Here’s the short version: yeast is a bacteria. It is common in the air and around most animals (including you and me). All it needs is an opportunity, the right media and a bit of time, and voila! Bread!
According to what I read on the Internets, mix two cups of flour (the kind without additives) with two cups of water in a bowl, cover the bowl with a cloth and leave it on the counter. Every day or so, discard half of the mixture and replace it with fresh. Before you know it, you’ve got your bread starter. Just mix it in with your flour when you’re ready to bake some bread and it will get to work transforming flat bread to full bread.
Of course, that leads us to a couple of questions. One, why is the Lord so dead set against leaven? After all, He created it in the first place. Two, what’s the deal with Pharisees and Sadducees? I mean, we’re all just people, right? Why can’t we just get along?
Then they understood that he did not tell them to beware of the leaven of bread, but of the teaching of the Pharisees and Sadducees. Matthew 16:12
Let’s start with Two, shall we? Those groups weren’t buddies. They came down on the opposite side of everything, but they are almost always found together opposing Christ. He had to deal with the P’s a lot, because they were the religious icons of their day. They wore the right clothes, had the right hair-cuts, and showed up in all the best synagogues, but it was all a big show. Jesus said they were like tombs, pretty on the outside but putrid to the core. The S’s on the other hand had the religious show down, too, while being practically atheists, refusing to believe in angels or miracles or life after death. Both of them had ideas very dangerous for Christians, because they seem reasonable on the surface but are both geared away from true worship, the kind that only occurs “in Spirit and in Truth”.
And One? Leavening agents are a link to yesterday. They are held over from the past, a reminder of our corruption. What God is changing us into leaves no room for ties to our sinful carnal nature. If we heed the worldly influence of legalistic ritualism or pragmatic compromise, we will miss the higher road to a real spiritual victory over sin and death. That’s why I say with the Psalmist:
Search me, God, and know my heart. Try me, and know my thoughts. See if there is any wicked way in me, and lead me in the everlasting way. Psalm 139:23-24