In Matthew 6, Jesus addressed three practices used by religious people to interact with God. Generosity, prayer, and fasting were three ways for people to show their devotion. Jesus had some harsh words for people who pursued these practices for outward recognition, and instead instructed his followers to do these three things "in the secret."
What does it mean to do these things in the secret? Is it necessary to always avoid recognition? Is it wrong to pray in public? What does it mean that God is "in the secret?"