Jesus feeds 4,000 in the Gentile Decapolis area, east of the Sea of Galilee. He contrasts this with a warning against the bread and leaven of the Pharisees. He gives good bread; they give crummy stuff.
He makes a point the modern reader doesn't understand easily. He fed 5000 in Israel and 12 baskets were left. He fed 4000 in Gentile land, and 7 baskets were left. These numbers are symbolic, based on the location. 12 is for 12 tribes of Israel: Jesus can feed all Israel. 7 is for the 7 Canaanite nations driven out by Moses, some of whom went to this region: Jesus can feed all the Gentiles. 5 might be for the 5 books of Moses, and 4 might be for the 4 corners of the earth. The point is that Jesus is the true Joseph, who can provide bread for the whole world, Jew and Gentile.
Jesus connects His identity with His coming cross and resurrection. This is what it will mean to be the Christ. It's totally unexpected, and Peter objects. Jesus notices Satan at work in Peter. He calls for everyone to note that we must take up our cross like Jesus will, follow Him, and not be ashamed.
The last verse assumes the divinity of Jesus.
Not noticing when we need to be fed by Jesus.
Thinking Jesus is like other religious teachers, when He gives real food and the others do not.
To resist Satan sometimes an extra measure of resistance or rejection of friends is needed.
Being embarrassed or feeling guilty when we aren't "winning" as Christians in the culture.