When lightning flashes, people can see it clearly. This is a metaphor for the way the Son of Man will appear: when he does, everyone will see him clearly. Alternate translation: "as the people can see lightning clearly when it flashes ... so they will clearly see the Son of Man" (See: [[rc://en/ta/man/translate/figs-simile]])
This refers to the future kingdom of God. Alternate translation: "it will be like that on the day when the Son of Man comes to reign" (See: [[rc://en/ta/man/translate/figs-explicit]])