Jesus continues His training of the disciples by reorienting them to the Kingdom. The worldly way of seeing the world and navigating life in it is upside-down and backwards from the Kingdom: last is first, die to live, deny self to gain, become like a child.
In the beginning of Mark 10, Jesus is confronted by the Pharisees about a theological debate in hopes of trapping Him. They hope however Jesus answers, He’ll paint Himself into a corner that will result in at least discrediting Him, if not having Him killed. They ask about legitimate divorce.
Jesus avoids the trap and points them back to the creation and institution of marriage, holding it up not as a disposable accessory but a God-given gift and treasure.