Leaven is an ingredient (yeast is a kind of leaven) in cooking that is often used to represent an influence of something in our lives spiritually or in general. The leaven causes dough to rise by fermentation (the process by which sugar is converted to carbon dioxide and alcohol...I know too much information:-). Leaven is also an element, influence, or agent that works subtly to lighten, enliven, or modify a whole (from dictionary.com).
It is usually used as an illustration in regards to either a good influence:
Matthew 13:33: He told them another parable. “The kingdom of heaven is like leaven that a woman took and hid in three measures of flour, till it was all leavened.”
or bad influence
Matthew 16:6 : Jesus said to them, “Watch and beware of the leaven of the Pharisees and Sadducees.”
Basically in Mark 8:15 the leaven of Herod and of the Pharisees might be an example of what Quintin was preaching about from Colossians 2:8: “See to it that no one takes you captive by philosophy and empty deceit, according to human tradition, according to the elemental spirits of the world, and not according to Christ,” last Sunday.
A philosophy that takes captive or empty deceit is the opposite of what Colossians 2:7 says, “established in the faith, just as you were taught.” So cling to Christ and faith, which we are taught in the Bible, in order that the leaven of erroneous philosophies, that take captive, and empty deceitfulness won’t rule us.
A few verses come to mind:
Romans 8:15: For you did not receive the spirit of slavery to fall back into fear, but you have received the Spirit of adoption as sons, by whom we cry, “Abba! Father!”
Galatians 4:7 : So you are no longer a slave, but a son, and if a son, then an heir through God.
Galatians 5:1: For freedom Christ has set us free; stand firm therefore, and do not submit again to a yoke of slavery.
In Christ we have a Spirit of adoption as sons of the living God, we are not slaves to sin, Christ has set us free from the slavery of these things. Let us fall in praise of God for His grace given through God the Son, Jesus Christ.
Ask yourself, "What is the leaven in my life?" I pray it's the kingdom of heaven and God's word!