17 - Jesus is transfigured so that His divine majesty pierces the veil of earthly things. Jesus heals a man; it required prayer and fasting. He predicts His death and resurrection. He pays the temple tax for Himself and Peter, miraculously.
18 - We must become as children to enter the kingdom. Take extreme measures to not cause anyone to sin. Jesus has come to save those lost sheep. We are to deal justly with those who sin against us, and forgive much as we have been forgiven even more.
19 - Is divorce allowed for any reason? God intends marriage to be permanent on earth, but our hearts get hard, so divorce is allowed (not required!) only for sexual infidelity. It is hard for the rich to enter the kingdom, but those who sacrifice here will be rewarded in the regeneration.