When they went across the lake, the disciples forgot to take bread. “Be careful,” Jesus said to them. “Be on your guard against the yeast of the Pharisees and Sadducees.” They discussed this among themselves and said, “It is because we didn’t bring any bread.” Aware of their discussion, Jesus asked, “You of little faith, why are you talking among yourselves about having no bread? Do you still not understand? Don’t you remember the five loaves for the five thousand, and how many basketfuls you gathered? Or the seven loaves for the four thousand, and how many basketfuls you gathered? How is it you don’t understand that I was not talking to you about bread? But be on your guard against the yeast of the Pharisees and Sadducees.” Then they understood that he was not telling them to guard against the yeast used in bread, but against the teaching of the Pharisees and Sadducees.

--Parallel verses:
‭‭II Peter‬ ‭1‬:‭5‬-‭9‬
For this very reason, make every effort to add to your faith goodness; and to goodness, knowledge; and to knowledge, self-control; and to self-control, perseverance; and to perseverance, godliness; and to godliness, mutual affection; and to mutual affection, love. For if you possess these qualities in increasing measure, they will keep you from being ineffective and unproductive in your knowledge of our Lord Jesus Christ. But whoever does not have them is nearsighted and blind, forgetting that they have been cleansed from their past sins.

Living a life following Jesus has been compared to a fish swimming upstream. It is a good analogy. The current of this world is guiding us towards worldly passions and instant gratification. Pleasures, rights, feelings, and self-knowledge rule the day.

God designed us to be in close communication with him and our brothers and sisters. As sinners saved by grace, we need to serve him well and also be alert to the temptations around us. Not focus on them, but be honest about them and plan against them.

What is so cool about how we defend ourselves from the world and its evil is we use the very things that also build us up. Prayer, the Word of God (referred to as the Sword of the Spirit), Honesty and Truth, our Salvation, the Pursuit of Righteousness, Repentance and Forgiveness, and Active Feet that Spread the Gospel (the good news about Jesus).

When we devote ourselves to these activities, our ability to follow Jesus and swim upstream in life is increased. It becomes doable, powered by his Spirit.

Jesus is warning his disciples here to watch out for false teachers and the direction they lead in. They mix lies into the truth, and like yeast’s impact on bread, it spreads quickly into the whole of our hearts.

The Bible is absolute truth and infallible in its wisdom. We must stand firm on its truth, love unconditionally and completely, even if love is hard or its application is tough.

So I must serve faithfully, and stay diligent in my faith. “The Lord is my strength and my shield; my heart trusts in him, and he helps me. My heart leaps for joy, and with my song I praise him.” (‭‭Psalms‬ ‭28‬:‭7‬)

Thank you, Lord Jesus, for your encouragement to be on guard against sin. Teach me to serve and love and diligently cling to your Word and prayer. With you I can swim upstream all day long!