("Whoever wants to be first must be last of all and servant of all", Mark 9:35)
"Jesus loves the little children" from The Chosen
Who is an important person (president, king, etc.)? — We consider those people as "the first" and us as second to them or "last".
Jesus doesn’t care about who is important in this world; what He cares about most is who helps others. / God does not care about who is important or rich or who is the oldest or the smartest — what He does care about is our goodness!
Concept of “winning” — Who likes to win at stuff?
He wants you to win at “serving/helping others” — because what He cares most about is our goodness!
Examples of serving/helping? — Examples: letting others go first or have a turn, saying nice things to others, etc. — "putting others first, putting yourself last"
-> “If you want to be first, you must be last” = If you want Jesus to look at you as a winner (as the first), you must show others that they are actually more important than you. That is really difficult sometimes, but that is what God cares about the most — our goodness.
Jesus is a funny king — He never wore fine clothing and a crown, He never lived in a palace. Instead, he was born as a baby among smelly animals and He did things like washing his friends' dirty feet. Not your normal king. I like to think of Jesus' kingdom as the "upside-down kingdom" — it's all kind of different from what we think it should be like. So in Jesus' Kingdom, the first are the last and the last are the first.
Final summary: He doesn't care about who is important or rich or smart; those people are not necessarily going to be the winners — He cares most about our goodness, so the people who are good and help others are going be the winners.