1 Corinthians 5:7-8 – 7 Get rid of the old yeast that you may be a new batch without yeast—as you really are. For Christ, our Passover lamb, has been sacrificed. 8 Therefore let us keep the Festival, not with the old yeast, the yeast of malice and wickedness, but with bread without yeast, the bread of sincerity and truth.
We are sinful people on our own. It’s natural and we we’re born into it. Anytime we don’t keep up our guard we allow the old yeast back in to spread and puff up. We need to stay in touch with our Lord.